http://finance.zacks.com/childrens-social-security-benefits-accounted-annually-9664.html
@lotsofquests, sounds like the use of that form refers to representative payees, if the child is under 18. To make sure the money is used for the child or saved until child is 18. But OP was 18 and got the benefit until he graduated high school I think.
@Kaponator, you said you had work income last year, was your EFC 0?