Yeah I've seen it too...
A couple years ago, I was shopping at Target, I saw a small child ( looks like he was 2-3 years old ) in the cart , he kept whining about wanting something off the toy shelf, the mother was getting soo frustrated with him, so she slapped him right across the face, and oh the child was screaming and crying, the customers around me were staring at her, I stood there speechless, cause I couldn't believe the mother slapped him soo hard in the face, then the child didn't stop crying, so the mother slapped him once more again, I felt so sick in my stomach and wanted to walk over there and beat the crap out of the mother for doing that, but I couldn't, I didn't want to get arrest, so I pretend I wasn't watching, saw the mother yelling at her son, I suppose she was telling him to stop crying, but he didn't....so I saw her lifting her arm up again, so I ran over there and grab her arm and told her " If you hit that child again, I'll call the police " She looked at me and start yelling, I didn't have a clue what she said, all she was doing was spitting crap all over my face" I never left I stood there and agrue with her, until the store manager arrived and I told him what had happened and then I looked at the mother and I told her " If I ever see you hit your son again, May God help me " then I left the store, I dunno what happened afterwards....If I ever seen a parents doing that to a child, I will end it, I don't put up with that BS! To me it wasn't discipling it was CHILD ABUSE!!!!