SSI stands for Supplemental Security Insurance. Child SSI is possible if the child in question fulfills the requirements. To apply for child SSI, the child may be as young as a newborn. There is no minimum age requirement, but there is a maximum age restriction. A child on SSI must be no more than 18 years of age, unless the child is attending school. In this case, the child may be up to 22 years of age. The child must suffer from severely or striking functional limitations. There must be documented medical proof of the physical or mental disability. This includes blindness and other types of disabilities as defined by Social Security Services. Considering the intricacies of the application it is best to consult an SSI specialist.