I get on buses every day - during the morning rush hour with lots of kids on board and in the evening although after the school-rush.

Have to say that I can't think of any instances where a kid deserved to lose their Oyster card. I'll moan that I can't get on a P4 during termtime because of them (but only in a half-hearted way since the traffic through the Village is so bad too that it's not a viable route except during holidays. Perhaps I've been lucky or just too engrossed in my book but for the most part, the biggest problem on our local buses is the sheer number of people trying to get on them rather than the types of people or their behaviour once on.