Everything you need to write a declaration letter to the judge in your custody case: an example, a downloadable template, an outline and tips. This article provides a comprehensive guide to writing a declaration letter for child custody cases, including a sample letter.To write a parent custody letter, you should follow a formal structure and clearly express your intentions. Here's a general outline to help you get started. The Virginia Judicial System has a number of forms for each court available on the court's form page. Use this free child custody agreement template to outline a comprehensive co-parenting agreement and parenting schedule. Agree on a Parenting Plan. If there is a Children's Lawyer or Child Advocates office, ask them to investigate. Ask them to present an opinion on which parent is best. To write a parent custody letter, you should follow a formal structure and clearly express your intentions.