It is possible to include a stepchild as a derivative beneficiary as long as (i) the child is unmarried and under 21 years old at the time of filing, (ii) the child was under 18 years old when the marriage took place, and (iii) sufficient documentation is provided, including but not limited to the marriage certificate, divorce decree or death certificate of the biological parent, and the child’s birth certificate and any other necessary proof of legal custody.