my 6yo saw them for the first time when she was five...she did wonderful! they had her look at a book and pick out certain pics to make sure she wasnt colorblind, and joked around with her during the actual eye test...they also didnt mind me in the room with her...it was great!
my son went to the eye dr. for the first time right after he turned one. She is specifically a ped. eye dr. and is used to seeing kids. it went fine for us. My older son was glad they had a waiting area with lots of toys to play with.