Parental kidnapping is when one parent illegally takes a child in violation of a court order. When non-custodial parents resort to parental kidnapping, they believe they are acting in the best interests of their children. In some cases, the act occurs immediately after custody is awarded to the other parent; in others, abductors find fault with the other parent for nonsensical transgressions. Anger is the prevailing motive for parental abductions.
Occasionally, judges do make mistakes and give custody to an unfit parent, or award unsupervised visitation, even if the parent is dangerous and has a history of problems. Parents unhappy with their arrangement should consult a lawyer and go to court to argue the need to modify their case rather than to try the system themselves.
There is no way to prevent your spouse from stealing your child. You can and should, however, take preventive measures which may discourage your spouse or, at least, give you leverage with police and the courts if your spouse goes ahead with their plan.
These ideas are what you need to know to be in the best position possible:
“    It is crucial that you have a clear, recent photograph of the child. Likewise, a list of distinguishing marks such as scars and birthmarks (or tattoos) is essential.   Many police departments offer fingerprinting for children. As basic as it seems, you should know the social security number of the child and the other parent.
“    Keep a list of the names and last known telephone numbers and addresses of family members and friends of the other parent who might provide assistance to the abducting parent or your client in the event of a kidnapping. In addition, if anyone outside of the family has shown an increased or unusual interest in the child, you should keep note of that person’s identifying information (name, address, appearance).
“    In every case in which you have a concern about kidnapping, contact the United States State Department to “flag” the child’s passport.
Parental kidnapping isn’t always as severe as it sounds. The simplest kidnapping is a refusal to return the child after scheduled visitation or temporary visitation. You know where the child is, but the other parent refuses to return the child. If it is during the school year and the child goes to school, you should pick up the child with or without the police and proceed to court to obtain a court order. This also constitutes contempt, because the failure or refusal to return a child at the end of court-ordered visitation or temporary custody warrants a right to file a Complaint for Contempt.

Take these precautions:
1.  Hire a Lawyer and get legal “custody” of your child – whether it is temporary or permanent.
2.  Think about getting counseling to work out differences with your former spouse.
3.  File a report with the local police stating the threats your spouse has made.
4.  Warn your children.
5.  Leave your custody order at your child’s school, day care center, camp, or with babysitters or after-school instructors.
6.  Stay on good terms with your in-laws.