Why do people hit children?

Yesterday i saw a friend who i haven't seen for awhile, catching up on her family how her youngest daughter had a baby last month and how her oldest daughter got out of a bad relationship last week.

It seems that the oldest daughter started to have a relationship with her brother in law (youngest daughters boyfriends brother) and that he is abusive and my friend was surprised that the daughter stayed in the relationship.

The eldest daughter has a son T aged 11 and a daughter H aged 6.

My friend didn't get to see these two grandchildren last Christmas and she wondered why. My friend told me how one day her granddaughter was at her house with some other family and while playing the other saw some bruises near her thighs and other parts of her body.

My friend not liking this went to talk to her eldest daughter to find out what had happened, it seems that just before the last Christmas H talked back to her mother and the boyfriend grabbed the child slammed her head into the bed quite a few times and hit her for a long time, at other times if he was angry he would get H and start hitting her for no reason.

To me people who hit children are cowardly.........the best treatment for any person who does that should be that they have to stand there tied up while someone bashes them for 10 minutes at a time, every week for a month and see how they like it...
.
.