There could be a variety of reasons why some people do hurt children physically. To some adults, it is a form of discipline, i.e,, to teach a misbehaving child a lesson. They expect the child to behave properly the next time around for fear of physical pain. However, this is taking the easier way which reflects the impatience and lack of compassion and genuine love on the part of the disciplinarian.
Others who do such deplorable act may have been victims of same atrocity themselves during their childhood,. Now, they are just repeating same pattern on their children. By virtue of such unfortunate experiences, they could have already regarded such violent act as a normal form of reaction or behavior by a parent.
Yet, nothing can justify any act of violence to children and regardless of the reasons, the persons concerned should think hard of their own motives for hurting children physically. They should really try to honestly confront their violent tendencies and should seriously seek professional help if necessary. Otherwise, it is more likely that the child would become another hapless victim who could victimize his own children later on. Thus, the behavior can be passed on and on.