Sitting still for long periods is naturally difficult for little kids. Of course they shouldn’t be allowed to go nuts, but a kid who just sits quietly for long periods with no signs of antsiness might be having their spirit crushed by authoritarian parents (or might just be unusually calm). Good parenting is a give and take.

The restaurant isn't going to complain about the kids chatting or pushing peas around on their plate. If the wait staff are willing to risk the ire of pissed off parents to say something, the kids must be going nuts.