Enforcement of child custody and visitation should be handled by a lawyer in family court. The police will generally refuse to get involved by saying this is a civil matter not criminal. What do you do if a parent or third party wrongfully withholds a child from the parent with custody or keeps a child beyond the time allotted for visitation?
There are two remedies available which are not mutually exclusive. The first remedy is to file a petition for writ of habeas corpus asking the court to issue a writ ordering the person holding the child to appear in court with the child and explain why the person has the child contrary to a court order. That is quick, easy and is supposed to take priority over all other proceedings in the court. This remedy usually results in return of the child.
The other remedy is to file suit for enforcement to hold the person (usually another conservator) in contempt of court for violating the court's custody order. This requires a hearing before the court. If found in contempt, the court may assess jail time up to 6 months and/or a fine up to $500 per occurence.
Both these remedies for enforcement of child custody and visitation are relatively complex procedurally and are not do-it-yourself propositions. Both these remedies will allow recovery of attorneys' fees.