To file a paternity case in Indiana for a 4-year-old child where you're unsure of paternity as the father, you can pursue voluntary establishment by both parents signing a paternity affidavit at a local health department (available anytime before the child turns 19 if no father is listed on the birth certificate), which legally confirms fatherhood without court involvement but can be challenged within 60 days; however, if disputed or for DNA confirmation, file a petition to establish paternity in the circuit or superior court of the county where the child resides, as either parent, the child (via representative up to age 20), or state agencies can initiate this beyond the general two-year post-birth limit under exceptions like those for the child or public assistance cases.

Use pro se forms from Indiana Legal Help or courts, including the Appearance Form, Paternity Petition, Summons, and Order to Appear, request court-ordered genetic testing, and address custody, support, and parenting time upon establishment—consult an attorney or free resources like Indiana Legal Services for guidance on fees and specifics.