How do I have my court ordered visitition enforced

You take them back to court for being in contempt of the court order, the judge may order them again, or set up a official place for them to leave the children for you to pick up. If they again don't allow visits, you take them back to court again, at some point the judge can start putting a money fine on each missed visit and/or put them in jail for being in contempt.

Depending on the state you live in you can also take the order with you to pick up the child / children and if the parent rufuses then call the police and they will have to relinquish them. I hope it never goes that far but it can.

Both of the above are correct. If the other parent refuses to let the child go, then you could try to call the police and have them go to the house with you. (my daughters father did it once). They really can't do much. All they will do is show the other parent the court order that states the visitation time. They will inform that parent if they refuse to let the child go, then they are in contempt of a court order. The other parent can still refuse, the police cannot forceably take the child. But you could then have the officer write a report and you would have proof that visitation is not being allowed. At that time, file contempt of court charges on the parent.