Children's SSI eligibility is based on a determination that the child has a physical or mental condition that severely limits the ability to function. Children receive SSI until they are 18 years old. If a child is ruled to still be disabled by the state at age 18 the SSI payments can continue. Children are defined as persons under the age of 18, and those under 22 that are not married and are full time students. The Social Security Administration determines eligibility of the child to receive benefits. Children who receive SSI are also usually eligible for Medicaid, even after the child is no longer eligible for SSI. Rules vary by state. Parents can act as the payees of their children's SSI benefits until age 18. Upon reaching 18 a child can receive the payments on their own behalf.