What happens if the non custodial parent refuses to return to the child to the parent with custody?

If you have a court order, you can call the police, have an escort of the police go with you to that parents’ house, show the police the order that the child to be returned with you and ask the police to affect the transfer. Now, no parents wants to have police involved so before you do that, ask the parent to return the child. If in fact the police decline to become involved, then you need to file an immediate motion with the court demanding the return of the child.