I'd say I see this from a separate perspective. While the kid might be a bit spoiled he also just wanted to ride, the parents didn't know that the kart they were buying was Chinese more than likely... a great deal of these websites and shops advertise their karts with American flags on them trying to pose their cheap kart as being quality.
Its a shame they destroyed the kart but you can understand their anger fully. Also there can be no straight determination that they own the digger. He may simply have a fantastic boss at a construction site that talks to his workers and understands the situation. The father might have just been a worker, to make an assumption otherwise is a bit off color.
At the end of the day the point is he wanted to ride, and he didn't stop riding the kart for lack of interested or that he wanted a 4 wheeler, they claim that he stopped riding because it never worked right. We've all seen Chinese karts fail randomly and they are not designed to take the test of time, everything down to the paint is horrible on those karts.
Understand that the kid really might be spoiled and that they might be filthy rich, but we don't know that off hand. The right thing would've been to put up a craigslist ad saying free Chinese POS to anyone who wants it, but not everyone is that way. Some people want vengeance.