Never. People are jailed for hitting children as it is illegal and we have already proven how traumatising it can be for the children. Any adult who could feel they need to hit their child to make them behave well clearly has issues of their own and doesn't have enough control. If the child really is struggling then doctors appointments should be made. Hitting a child to force them to behave would only make them rebel in a way to punish or just out of hatred.