Many forms in Texas are not available in a fillintheblank format. These forms and instructions are available in the General Clerk's Office, Room 108, in the Nassau County.This guide includes forms and instructions for a letter and affidavit to request that the court register an out-of-state custody order in Texas. Petition for (Custody) (Visitation). This guide tells you how to ask for a custody, visitation, child support, medical support, and dental support order. A petition for custody would be filed in the juvenile, family, or domestic relations Court with jurisdiction over the child, at the county level. File this form when you and the other party cannot agree to a temporary arrangement for parenting, child support, or other issues before the final hearing date. I understand I must fill out and attach a Declaration in Support of Changing. Primary Custody within One Year form to this Petition. This online program from Family Legal Care guides you through filling out a Petition for Child Support.