Child Support Forms ; 4-3b. Addendum to Support Petition– Request for Child Support (IV-D) Services.Petition for (Custody) (Visitation). To fill out the Supplemental. Petition, start at the top and fill in the blanks. The forms below are some of the most common forms used in the Domestic Relations Division, but there are many more. This online program from Family Legal Care guides you through filling out a Petition for Child Support. This document provides an overview of the basic steps to file for custody of a child in Cook County,. Illinois. How exactly do you file a response to a petition to modify child support in Illinois. Download and complete Divorce, Child Support, and Maintenance forms from the Illinois Office of the Courts.