Sounds like you're guessing.
Sounds like you're guessing, too.
So, since everyone's geussing...
Why are the parents less culpable than WAL-MART?
Maybe they should sue themselves for incompetence.
Why must we believe that the kid took the correct action to apply the type of brakes with which this bike is equipped?
Maybe the brakes DIDN'T "fail"; maybe the kids attempt at trying to apply them "failed". Since this was a different bike than he was used to riding the braking system could very easily be different from what he was used to. In a moment of panic, trying to apply the coaster brake on a bike with handbrakes is a guaranteed "fail" situation.
Of course, I'm just guessing...
At least THAT'S free.