If my ex-husband did not return my children to me per our divorce decree today at 8:00 am, how do I get them back if the police will not help?

If you have a certified copy of your custody/visitation orders that clearly state when the children are supposed to be returned to you then the police should enforce those orders.  If they refused, and your ex did not return them, you need to sonsult a lawyer in your area to find out how to get your children back.  If you have an enforceable (meaning it is very clear as to who the children should be with and what time they should be returned) order and it is a certified copy and a police officer refused to help I would contact his/her superior all the way up the chain of command until someone did something.  Their job is "law enforcement" which also means enforcing a valid court order.