I don't know about you, but I've had to work on every bike I've ever come to own before I rode it. With new bikes, the brakes are pretty much always too tight, resulting in a nice toss over the handle bars. It doesn't hurt to check. If the kid had, he would have caught the problem. This kid's a moron, and his mother too.
I couldn't put a bike together if my life depended on it so I can't comment on mechanical issues and will defer to your opinion.
I just wonder how old the child was and if the bike had been ridden prior to this accident.