my ds2 is 2.5 and also screams the house down when i wash his hair. It's so bad i only do it once a week. I try to do it right at the start of his bath, then after I've washed and rinsed i distract him with high 5's and praise for being a brave big boy. Worked last week, he was fine after that. But it's an ongoing battle. He hates the hairdresser too. I have his daycare provider pushing autism onto me even though he's fine in all other ways. It's comforting to know there are other kids the same out there.