You're not kidding. Definitely a minefield. Normally I'd let it go but that sounds particularly cruel and vicious. I think I would have had to have said something but I'm pretty damned sure I would have got a mouthful back and told to mind my own business but least I would have had my say. My mother would give me a good whacking when I misbehaved but when those kids have clearly not done anything wrong as you say, and the fear in the child's eyes it sounds like they get beaten on a regular basis and that's child cruelty to me. There's not a lot you can do really.