Not even kids in general, just British kids in particular.

Well that's the thing: William Golding was a self-confessed misanthropic depressed alcoholic who really didn't think much of the British schoolchildren he taught, and didn't think much of previous "stranded children" stories, and wanted to write one where the kids would act way he saw children act. It must also be remembered that he was writing in the shadow of the WW2, which showed just how terrible human beings can be to each other.

My own sister is a teacher, and the way she talks about her students, I think if they were in that situation they would be even worse.