depends on your purpose

If you want to have some leverage over your hu*****and (for future divorce or settlement,etc.), call the police no matter how light your hu*****and hits your child.

If your purpose is solely the well being of your child, if the hitting is not that bad, just talk to your hu*****and before calling the police.  Also talk to your child first as well.

If the hitting is pretty bad, call the police.