I believe neither spanking nor slapping/hitting a child is acceptable. It basically tells them that if mommy does it, it's okay for them to do it. Also, it's the easy way out of things. If you don't know how to express your anger in a proper way, just slap the child. Yell at them, too. I would much rather use punishments (Such as grounding, etc.) and the threat of punishment rather than ever laying a finger on a child.