There's a new rule I saw enforced on a flight recently - a mother was travelling with a kid who was 13, and they were both in an exit row. During the briefing, the FA asked how old the kid was and said he had to move back.

The FA then came back and said they *both* (mother and kid) had to move - a parent cannot be in an exit row when they have a child elsewhere on the plane. I'm guessing that during an emergency, the parent would be more concerned with finding the kid than helping an evacuation.