The order you were served with (or will be) should include instructions on how to challenge it. There is usually a limited amount of time to register a challenge. If you do not yet have the order, the advice is the same: Consult a lawyer for help in challenging the order. Particularly given that you wish to make a chid visitation case, it's important to take action, and this is a strong warning that your ex- will be taking a "no holds barred" approach to fighting any visitation petition you file.

