I'm assuming he has them for Christmas break.
I think it is cruel but unless he is ordered to let you talk to them on the phone and to give you the address of where they are at Christmas then he is not technically violating a court's order. You will have to read the court order that the judge signed. I have not seen your court order so I'm only guessing that it does not contain those provisions. Most court orders do not automatically contain provisions that the parents must notify the other parent of where they are going for visits.
But the court orders do require each parent to keep the other notified of their current home address and phone numbers so that they can contact each other in case of an emergency regarding the children. Also, often there is a provision that the parent not in possession of the children is allowed phone access during specified times.
I hope this information is helpful.
If you don't understand your current decree then you need to call your former attorney. If that attorney is not available, then you might want to look on this website and select an attorney in your neighborhood to read your decree and explain it to you. It is definitely worth an hour of an attorney's time to go over your decree with you.
I hope that you are able to have a Merry Christmas.