Hang in there. There'll be tons of threads like this closer to Christmas as schools have their nativities. 
FWIW, I try to keep a balanced view. Yes, children should be quiet. Perhaps the food wrappers were to give food to the small children so they WEREN'T talking, in which case, at least an effort is being made. And if all else fails, parent should take child out, so as not to disturb others.
That being said, if it's a school function, it's always nice if the school can do more than 1 performance, so one can be designated as a "child-friendly" performance.
If it's not school and it's aimed towards children, then I suppose some minor disruptions are to be expected, although constant talking should be addressed. However, obviously keep in mind that some children have SNs and cannot control some of their behaviour and there is a need to be tolerant to some degree - especially as you have no idea which children have SNs and which do not. Psychic knowledge such as "oh I think it would be obvious" or "I know everyone in the world and there's no way this person has SNs" don't count. Children with SNs have a right to see the concert as well.
There. I've placed myself firmly on the fence. 