I can't think of any children at a young age (8 or 9, sure but 2 or 3, no way) that you can say no to once and they understand it. You have to reinforce EVERY time what is and is not acceptable until they get it. I remind my daugher EVERY flight not to touch the seat back. I do try to book 1E, F whenever possible but that's because of me, not for her benefit - I would prefer the under seat room for her toys and activities that I don't have in bulkhead.