Actually not the young the better. Rule based reasoning and social awareness only start about 3 and half to four and around 3rd for awareness of society. Hitting does nothing before 4 except cause fear and resentment in the child, and many scientific studies bear this out. It is a fact that the brain expands so rapidly in size and in function, that all the memories stored up to the age of three are permanently erased by three due to that brain growth. The only real thing hitting children (or spanking as most people call it) is teach adults that it is OK to lose your self control and hit someone one pounds lighter and feet smaller than themselves. On the playground that is called bullying.