Why are you allowed to punish your children when they misbehave but when you do it to your wife...?

If your child is acting up you have to discipline them. Sometimes physically by bending them over and spanking their supple and soft posteriors. Spare the rod, spoil the child. The Bible advocates this. So when your wife is misbehaving it is naturally assumed that you as the head of the household have to punish her as well. But people seem to miss this point.