"They must have been working in a group and casing places out. There were lots of knots they would have had to untie, they would have taken their time doing it otherwise they would have made a lot of noise. One of them would have had to lift the trailer, while the other rolled the bikes off.
"It's pretty disheartening for a 8-year-old kid to have this sort of stuff happening to him."
Campbell said riding his motorbike was his "favourite" thing to do and wants to start racing motorbikes soon.
The 8-year-old said he and his friends at school felt "angry" when he found his bike stolen.
Mr Dean said about a month ago Campbell had a scooter stolen from his mother's house, while a number of other items, including an X-box have been stolen recently.
"I hope we get them back, or what's he going to think about what society is like?"
He said it was "disappointing" knowing that the thieves would sell the bikes for "next to nothing" as soon as they could.
"I shouldn't have to work my ass off to have stuff like this just flogged. I guess I was too trusting.
"I'll have to lock them up inside the shed now and chain them up."
A $500 reward was offered by Mr Dean if the two bikes were returned, which he valued at about $1700.
"I'm happy to pay a reward if we can get these things back, it will be worth it to make him (Campbell) happy again."