My son is 8.5 months old and has 6 teeth. Should I be brushing them? He literally screams at me when I try to brush them - with proper tears and everything. He's quite happy to play with the toothbrush when he's given it, so I know he doesn't hate the taste of his toothpaste or anything like that. He has only started the screaming in the last couple of days. Very annoying! What should I do?