My 3 year old niece just started school this month, in the asd class. Her parents were sure she would not wear a mask, but after the first day, she seems to do it happily. She sees her big sister do it, and she gets plenty of praise for wearing it. Try having the whole family wear a mask at home first, so it seems normal. Get a cute one with a picture of something he likes on it.

Thanks. Will try that this weekend and just keep trying...