What about in Deathly Hallows? Spoilers below!
In Deathly Hallows Lily flies through the air when she jumps off the swing and shows Petunia how she can make a flower open and close itself at will. That she does on purpose. And that's definitely canon, and although Lily was remarkably clever, probably not that unusual.
I don't think it would be so strange if the kid even does it on purpose. If he's as old as 10, he's probably done accidental magic before now.

:S