My son is turning three on the 11th of nissan and we can’t give him a haircut before Pesach. Can I cut his hair on Chol Hamoed or during the Omer?
You should have a lot of nachas from him.
Regarding your question, you can not cut his hair during Chol Hamoed, because we are not allowed to give haircuts then. If your minhag is to start the omer from Rosh Chodesh Iyar you can give him his haircut then, but it is better to wait until lag b’omer.
Shulchan Aruch 531-2.