Harry, 15, discovered his beloved KTM 85 and CR 125 were missing about 12.30pm on Monday.

The bikes had been tied-down on a trailer in their Golden Square backyard which is fitted with security lights and a high fence.

His family say they feel violated and angry about the theft.

The motorbikes were worth about $9000.

Without a bike Harry will no longer be able to compete as his family is unsure if they will be covered by insurance.

Harry's mum Sally described the theft as "devastating".

"They obviously knew what they were doing," she said.

"They've obviously seen us coming in and out and know where the bikes are.

"It's just sickening to think they've been watching us.

"We are absolutely distraught.

"We were all up last night, none of us have slept.

"We were frightened they were going to come back last night.

"We're all looking out the windows, we can't trust anyone."

Harry has been riding motorbikes since he was two.

"I've gone through about 15 bikes and I've broken both my legs, one arm and my sternum," he said.

"I went A Grade when I was nine or 10."

But without his bikes and unable to afford the cost of replacing them, Harry fears his involvement in the sport might have come to an untimely end.

His mum Sally broke down in tears as looked at shelves ladden with Harry's trophies.

"I've just given him a life with these bikes," she said.

"I work for the bikes and these people just came in and took it all away. I just don't know what to do."

Sally said people had already come forward with offers to lend Harry their motorcycles.

"A guy from Ararat that rides in Maryborough told him you can have my bike for the next club day, you need to race," she said.

"People are very generous."

Anyone with information should phone Crime Stoppers on 1800 333 000 or Bendigo Police on 5448 1300.