If your child experienced a hitting stage, when did it start, when did it end, how long did it last, and any unique tips on helping it stop ASAP?

It's been going on since 17m and he is 26m now so I am losing hope. LO2 was born 2 months ago and he hits her in the FACE 1-2x a day despite our best efforts. He hits us too and other kids sometimes.

I've posted about this twice so far but I'm more focused on numbers now, rather than behavioral managment.