I had a similar situation with my 2YO last year... she kept hitting her (tiny baby!) sister on the head, and would get disciplined for it, after which she would just do it again.
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I don't know enough about your situation to say, but in our situation our daughter just LOVED the repetition and routine so much, that even if it were a negative thing, she'd want to repeat it over and over because she loves routine.
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So the way I fixed it (which was hard) was just to break the cycle. Â For a whole week I didn't let her play with her sister at anything approaching close range. Â Didn't make a big deal out of it, played happily, just made sure she played a few feet away. Â After a week, I slowly started letting her back in her sister's space, and she'd forgotten the cycle enough that the hitting was gone.
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Maybe you could work at keeping him away from all hair and faces for a little while? Â See if he forgets the pattern?