The body of the five-year-old boy was pulled from the river at Moama on Saturday. His nine-year-old brother remained in a serious condition in hospital on Sunday night following the incident.

Police allege their mother, who cannot be identified for legal reasons, held both their heads underwater, but the older boy managed to escape.

The boys' grandparents are furious at government agencies, believing they failed the family and could have done more in the lead up to the tragedy, said Dale Brooks, a lawyer for the family.

"Family and Children Services and Corrections have failed the family miserably," he said.

NSW Premier Gladys Berejiklian said all agencies involved in the mother's case are now under investigation over the tragic incident.

"We've asked for all of our agencies to give urgent reports on what they knew," she said on Sunday.

"We will be instigating investigations, but also co-operating with all the authorities, to make sure we get to the bottom of this."

She said it was "absolutely devastating" to hear of the circumstances of the child's death.

"I want to extend my deepest condolences to the family. I can't imagine what they'd be going through at this time.

"And I want to give them an assurance that we will make sure all of the agencies look into the matters as appropriately and as quickly as possible."

Police divers discovered the younger brother's body in a section of the river near Moama about 11.35am on Saturday.

The mother handed herself in to police at Echuca on the Victorian side of the river about 10pm on Thursday, police said.

She has been charged with attempted murder, and in a brief hearing in her home town of Deniliquin, 77 kilometres north of the scene, the court was told she is likely to be charged with more offences.

She did not appear in person, and is scheduled to appear by video link from a prison in Junee on Monday.

The older boy suffered serious bites from a nearby dog and was taken to the Royal Children's Hospital in Melbourne.

The dog was seized by the Murray River Council, but its owners have demanded it be returned as they believe it was only reacting to the incident and did not intend to hurt the boy.

Calls to the Murray River Council were not immediately returned on Sunday.

 – The Age

UPDATE 12pm, March 5: Police have formally identified a body recovered following a search of the Murray River as that of the missing five-year-old child.

Deniliquin police Inspector Peter Hayes told the Riverine Herald local officers were able to identify him because they knew the little boy. 

“Which saved the grandparents having to come up and do it,’’ he said.

The grandparents remain with their nine-year-old grandson at the Royal Children’s Hospital in Melbourne, the Riverine Herald reports.

The boy, who was bitten by a dog on the banks of the Murray and rescued by the dog’s owner and his friend, is in a serious but stable condition.

- Riverine Herald

UPDATE 4pm, March 4: A child’s body, recovered from the Murray River this morning, has been transported to Deniliquin.

Police told the Riverine Herald they would conduct the heartbreaking process of family identification there, before a post mortem in Newcastle. 

Counselling is being offered to emergency services personnel involved in the search after many of them broke down, overwhelmed by the discovery. 

Police believe the body to be that of a five-year-old boy, reported missing following an incident at the Murray River in Moama on Thursday. 

New South Wales police said the boy’s nine-year-old brother remained in a stable condition at hospital in Melbourne.

A 27-year-old woman has been charged with attempted murder in relation to the nine-year-old’s injuries. 

Police expected further charges would be laid when she next appears in court on Monday, March 6, at Deniliquin Local Court. 

The woman is expected to be transferred from Deniliquin police station to Junee Correctional Centre, Fairfax Media reports.

- with Riverine Herald and The Age

UPDATE 12.37pm, March 4: Police have found a child’s body following a search of the Murray River.

New South Wales police said they were told a five-year-old boy was missing in the Murray River at Moama on Thursday, which started a search operation involving police from Deniliquin Local Area Command, SES, and Maritime Rescue, and the Victorian police airwing and divers.

A child’s body was found in the water about 11.35am today and has yet to be formally identified.

However, police believe it to be that of the missing five-year-old.

The boy’s nine-year-old brother remains in a stable condition at hospital in Melbourne.

Police said a 27-year-old woman appeared via audio-visual link in Deniliquin Local Court today, charged with attempted murder in the relation to the injuries sustained by the nine-year-old.

She was refused bail during the court hearing.

Police said should would reappear, via audio-visual link, at Deniliquin Local Court on Monday 6 March.

Further charges are expected to be laid at that time.

An emergency services officer told the Riverine Herald he was overcome with emotion when the child’s body was recovered. 

“He was so little, it was awful, the whole thing has been awful, and everyone here is devastated,” he said.

“All of us have been hit so hard.

“This is a tragedy not just for the family but the whole community.”

- with Riverine Herald

UPDATE 9am, March 4: The search for a five-year-old boy missing in the Murray River continues, with police divers from New South Wales relieving those from Victoria this morning. The child has been missing since Thursday.

UPDATE 4am, March 4: A mother has been extradited to NSW and charged with attempted murder after she allegedly tried to drown her two sons in the Murray River, leaving one boy in hospital and police searching the water for the second. She has been refused bail and will appear in Deniliquin Bail Court today. 

UPDATE 6pm: Lawyers acting for the grandparents of the children involved in the incident in Moama have released a statement, claiming they alerted authorities to the “imminent risk” to the children following their mother’s release from prison.

The statement from Brooks Hall Lawyers is as follows:

We can confirm that we act for the grandparents of the children involved in the tragic events in Moama yesterday. 

The grandparents have had full-time care of the children for close to 18 months.

We had made considerable representations to Family and Children Services and the Department of Correctional Services about the imminent risk posed to the little boys with their mother’s release from prison. 

Both departments failed to act and consequently we now have a grieving family.

We enclose a copy of the letter sent to Albury Community Corrections Office only yesterday and the Apprehended Violence Order held by our client against the mother who has now been charged with attempted murder, with her other child still missing.

We can confirm that we have been contacted by Family and Children Services today to commence processing a working with children’s check for the grandparents.

We ask that the privacy of the family is respected at this very difficult time.

A letter sent to the Albury Community Corrections Office on Thursday was also released to the media.

The letter details allegations that after the mother was released from jail in February, she was taken to the grandparents’ home “with no regard for the AVO in place protecting our client”.

The letter claims an officer from the Community Corrections Office said they would only act if threats or intimidation were made.

It also states:

“We advise that the daughter has now snatched the grandchildren and taken our client’s motor vehicle interstate without the consent of our client and in breach of the parole conditions. Our client has been left distressed and without any assistance from your office since the children disappeared.

We are instructed that our client holds the Department of Community Corrections and the Police responsible for the present situation for their lack of communication and support in essentially off-loading the housing of her daughter to our client. They have further exposed our client to violence and physical harm.”

UPDATE 4.50pm: A woman police believe attempted to drown two of her children in the Murray River at Moama will be extradited to New South Wales.

The woman appeared by video link in the Bendigo Magistrates' Court just after 4.30pm, where the extradition was granted.

She sobbed uncontrollably as Detective Sergeant Trent Swinton read out the details of her alleged offending.

The court heard the mother arrived at a property on Perricoota Road - adjacent to the river - in the mid to late afternoon on Thursday with her two children, aged 9 and 5.

Police allege she told her eldest son to get in the water and attempted to drown him.

Detective Sergeant Swinton told the court the younger son was screaming during the incident.

The woman then allegedly turned to the younger son, while the older son managed to struggle free before he was attacked by a dog.

The court heard the youngest son was last seen drifting face-down in the water.

The older son was "savagely mauled" by the dog and was airlifted to the Royal Children's Hospital in Melbourne. Screams were heard by people on the riverbank who did not witness the incident, the court was told.

Detective Sergeant Swinton said the woman made full admissions to her role in the incident, and told police of her "intention to kill both children".

The court also heard she allegedly told witnesses the night before that she "had to drown my babies".

No application for bail was made, and the mother was transferred into the custody of New South Wales Police.

She will appear in the Deniliquin Local Court tomorrow.

UPDATE 4.20pm: The woman is currently facing a Bendigo court via video link from Echuca.

NSW Police is applying for the extradition of the woman to NSW on an arrest warrant for attempted murder.

Once granted, it's expected the woman will be taken to Deniliquin where the warrant for attempted murder will be executed.

NSW Police anticipates the woman will be refused bail overnight to appear in Deniliquin Bail Court tomorrow.

Meanwhile, a Royal Children's Hospital spokeswoman says the nine-year-old boy remains in a serious condition.

UPDATE 1.30pm: A mother who allegedly tried to drown her two sons in the Murray River was reportedly released from jail two months ago.

New South Wales police are in the process of extraditing the woman, 27, and preparing a charge of attempted murder.

One boy is in hospital and police searching the water for the second. 

Deniliquin local area commander Paul Condon said police believed there was still “every chance” the five-year-old would be found alive.

“We all live in hope,” he said.

Superintendent Condon said the “devastating” incident would likely “rock the community of Australia”.

“It’s a terrible story, it’s a sad story, it’s a tragic story, not only for the community, the police, but especially the family, it’s just terrible,” he said.

“Things like this happen and it’s devastating, it’s not only this town, but the whole local area command, NSW and Australia.”

A visibly emotional Superintendent Condon said all emergency services workers involved in the search and investigation had been affected by the incident.

“Police are devastated, the community is, it’s something someone has to do and we’re the people – and so is the ambulance and the fire brigade – we’re the people that need to do these things, someone’s got to do it and my people do a really good job,” he said.

Superintendent Condon said the nine-year-old boy was initially taken to Echuca Hospital by nearby residents. 

“He’s required some surgery on the dog bites at this stage and of course he’s distressed, he’s a nine-year-old boy,” he said.

UPDATE 1.20pm: The woman, from Deniliquin, is in hospital undergoing assessment after handing herself into police at Echuca on Thursday night. 

Fairfax Media understands police will allege she told her family yesterday that they would never see her sons, aged 5 and 9, again. 

She then allegedly travelled more than 70 kilometres from Deniliquin to a part of the Murray River near Moama, on the NSW-Victoria border. 

As she was allegedly drowning her sons, a pit bull dog belonging to a nearby resident was somehow alerted to the commotion and became involved. 

It is understood the nine-year-old boy sustained several dog bites but it allowed him to escape the water. He is in hospital in a serious condition.

The five-year-old son is still missing. A search by NSW and Victoria police, SES and Maritime Rescue commenced on Thursday evening but was called off at 11pm, before being restarted at 8am on Friday.

Victorian Police divers and spotter planes are also taking part in the search. The Riverine Herald has reported police have already recovered a small T-shirt from the river.

The situation unfolded at 7pm on Thursday, when police were called Perricoota Road, Moama, where a nine-year-old boy was found with serious dog bite injuries.

He was rushed to hospital in Echuca before being transferred to Melbourne for further treatment.

Shortly after that police received information the boy's five-year-old brother was missing in the Murray River.

Sometime after 8pm Thursday, the children's mother wandered onto a property near Moama where she had a conversation with a man who then drove her to the Echuca police station, the Herald has reported.

The woman was arrested after she presented herself to Echuca police on Thursday about 10pm. 

She was admitted to hospital and received treatment for a dog bite. She has since been released.

The children were not formally in the care of their mother and were being cared for by their grandparents, the Herald has reported.

In October, police in Echuca released the woman’s photo as part of an operation to crack down on outstanding warrants. She had two warrants out for her arrest at the time. 

In a statement, Deniliquin local area commander Superintendent Paul Condon said no other parties were being sought in relation to this matter.

"The dog belongs to a local family and police and emergency services were contacted by a local resident," Superintendent Condon said.

"Contrary to rumours, the dog was not set on the child.”

UPDATE 12.10pm: NSW Police has released a statement this afternoon saying the woman was also treated for a dog bite overnight.

The woman – who is also the children’s mother – was admitted to Echuca Hospital after she presented herself to Echuca police about 10pm.

She received treatment for a dog bite and has since been released from hospital.

The woman is assisting detectives from Deniliquin Local Area Command with their inquiries and it is expected NSW Police will be applying for her extradition.

Deniliquin Local Area Commander Superintendent Paul Condon said no other parties were being sought in relation to the matter.

“The dog belongs to a local family and police and emergency services were contacted by a local resident,” Superintendent Condon said.

“Contrary to rumours, the dog was not set on the child. This has been an extremely traumatic scene for all the first responders involved and welfare support is being offered.’’

Police are urging anyone with information to call Crime Stoppers on 1800 333 000 or use the Crime Stoppers online reporting page: https://nsw.crimestoppers.com.au/ 

UPDATE 11.45am: The 27-year-old woman – and mother of the two boys – is expected to face a charge of attempted murder, the Riverine Herald is reporting.

NSW detectives, part of Strike Force Bulletin, have arrived at Echuca police station and started interviewing the 27-year-old Deniliquin woman arrested there late last night.

They are wanting to talk to her about the disappearance of her five-year-old son and the injuries to her nine-year-old son.

It is believed the children were not formally in the care of their mother at the time she collected them from Deniliquin last night and were being looked after by their grandparents.

Strike Force Bulletin was set up soon after the first reports of the incidents in Moama were made known to police.

Earlier on Thursday NSW police had issued an appeal for help in locating the woman and her children, saying they had “serious concerns”  for the welfare of the mother.

Once the woman arrived at Echuca police station around 10pm that post on the NSW police Facebook page was taken down.

It is expected the woman will be charged later today and once she appears in court NSW police will apply for extradition.

Victoria Police divers are continuing their search for the five-year-old boy, appearing to have already recovered a T-shirt.

The nine-year-old boy remains in a Melbourne hospital after being attacked by a dog on a riverside property near where his younger brother was last seen about 7pm Thursday.

The owner of the dog involved in the incident said she cannot believe her dog attacked the boy.

She said her four-year-old pit bull lives with young children and was more likely reacting to the drama going on at the edge of the river.

In her opinion she believed her dog might have actually been trying to pull the nine-year-old to safety, not attack him.

- Riverine Herald

UPDATE 10.15am: The woman remains under Victoria Police guard at Echuca Hospital this morning. 

Fairfax Media understands the woman and the two children were all related.

A police spokesperson said no other parties were being sought in relation to the incident.

She is expected to be extradited to New South Wales today.

VIDEO: Courtesy of the Riverine Herald.

EARLIER: A five-year-old boy is missing in the Murray River and a nine-year-old boy has been hospitalised with serious dog bite injuries overnight.

New South Wales and Victoria police, SES and Maritime Rescue will resume searching for the younger boy at 8am after the search was called off at 11pm on Thursday.

The search, near Moama, will also involve Victorian Police divers and airwing.

It follows police being called to Perricoota Road, Moama, at 7pm on Thursday where a nine-year-old boy was found with serious dog bite injuries.

He was taken to Echuca Hospital and transported to Melbourne for treatment.

Shortly after police received information the five-year-old boy was missing in the Murray River.

A 27-year-old woman related to the children was arrested and is assisting police with inquiries after she presented herself to Echuca police on Thursday about 10pm.

In a statement, Victoria Police confirmed they are assisting with the search.

“Victoria Police is assisting New South Wales Police with their search of the Murray River,” it said.

“Our Air Wing was doing searches from the air last night and our Search and Rescue Squad is attending this morning.”