Payments upon turning age 18

Here is an excerpt from What You Need To Know When You Get Social Security Disability Benefits

When a child reaches age 18

A child’s benefits stop with the month before the child reaches age 18, unless the child is disabled or is a full-time elementary or secondary school student and unmarried. About three months before the child’s 18th birthday, you will get a letter explaining how benefits can continue. We also will send the child a letter and a student form.