Seems to be a phenomenon that has only become acceptable in the past couple of years. I'm sorry but it is RUDE, however young your child, to sit listening to or watching something without headphones. It happened recently on a Club Europe flight where a guy was playing a game on his iPad which was making very loud noises. I politely asked him to switch the sound off and he did, but I struggle to understand how people can have so little self awareness or consideration for those around them.