This chapter of the Texas Family Code describes who can file a SAPCR, how they must do so, and what the petition must contain. Texas Family Code, Chapter 103.The primary form you will need is a "petition" for a suit affecting the parent-child relationship. This form asks for basic information about both parents, your child, and the type of custody arrangement you are seeking. 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. Step 1: Fill out the court forms. Filing the Initial Custody Papers. To begin filing for custody of a child in Texas, you must complete and file the appropriate court documents. Texas law recognizes two types of legal custody: joint and sole. If you need the court to decide how your children should be cared for throughout the legal proceedings, file a motion for temporary orders.