While there are a percentage of "demon children" the vast majority are basically well mannered. I do take exception when someone complains about the "noise" when children are merely playing. They sure can handle the pool music and the loud pool games but if a child laughs too loud or makes a basic kid squeal when playing in the pool they act like they just had their ears blown out by a 138 decibel jet engine.
Children should know how to behave in the dining rooms and other venues and if they don't the parents need to remove them from those venues.
I still have to maintain that on all of my cruises I have never had an issue with a child but I have had a few with obnoxious people who believe no one should interfere with "their" idea of a vacation. That idea is that the ship is their private yacht and no one else should impose themselves on that idea. I also have seen many "nice" adults become total jerks when they've had a few too many drinks of the day. I wish these people had "parents" onboard.
Overall I'll wait until the kid or the person does something that is actually bad before I pass judgment or change tables.