Kick your child just for the fun of it....

A married couple we know had a young daughter of just 4-5 years old. We met the family on the beach and the father played with his daughter. Suddenly he start to kick her behind so she falls in the sand on the beach. He laughs. We cannot understand his behaviour and the mother does nothing. The little girl does not understand either. She gets up and he continues to kick her behind so she falls. He laughs. Some people were not made to be parents...I wonder what he would feel like if his daughter made a move as in the photo..??? Just for the fun of it!