How can I get a court order enforced on parenting time, when police tell me they can't enforce it??

When a party subject to a court order fails to obey the order, there are remedies. If your ex boyfriend does keep your child, and you know where they are, you should be able to call the police and enforce the order. Of course, if you don't know where they are, that won't work. You can bring a contempt of court action against your boyfriend for violating the court order. Your ex risks being fined or put in jail or both. The real issue is how to be proactive. You have time to consult with an attorney and have a letter written to your ex by your attorney. That letter needs to state emphatically what will happen should court orders not be obeyed. Good luck- usually people who intend to ignore rules, orders and boundaries need just one appearance before a judge and some time in jail to get them to understand. I do suggest a consult with a family law attorney to address the situation proactively. It could be very distressing for a 15 month old toddler to be away from his primary caretaking parent for 3-4 nights. He has no way of understanding where you have gone.

Your question is unclear. How will your boyfriend try to exercise his parenting time if he is out of town? What part of the order do you want to have enforced?