I thought that at 10 months a child didn't really know what it was doing, however my DD seems to know what she wants and hits out if she doesn't get it. I imagine that she has learned all she knows from her 2.5 year old brother!
Anyway, I am not really sure how to deal with it. If DS isn't around, I try to ignore it. For example today she scratched my arm, looked at me for a reaction and then did it again, I just ignored her. But, if she hits DS, I cannot really ignore it. When he grabs toys from her she aims for his face and I can explain it to him, however sometimes he is actually being kind and she goes for the left hook on the cheek too.
I feel really lost with this as I want to nip it in the bud, but I am unsure how.