My DS has been described as "hard work" and "challenging". And yes, he can exhibit these bad behaviours. But I don't ignore it. DS is stomped on. I encourage him to be himself and enjoy life, but be mindful of others and a young gentleman. If he threw food, tore up others' work and made a baby cry, I would be having serious words and DS would sort out the consequences. What is the mother doing about her daughter's behaviour? Sounds like very little or your DD wouldn't be trying it on for your reaction. (And why are you ignoring this too? I have no qualms in telling other children off if they're upsetting my DS, just as I'd tell of DS for upsetting another child.)

But then that's part of the reason I didn't have a baby to deal with when he was younger!