To qualify as a child for TANF, an 18 year old must go to high school full-time. A vocational school that is equal to a high school counts, but GED classes do not. A residential program that provides a regular curriculum of instruction equivalent to that which leads to a high school diploma also counts. See PM 03-04-02-b for the meaning of full-time school.
A child who is a high school graduate no longer qualifies when they are age 18. An 18 year old who is not in high school full-time does not qualify as a child. The child remains eligible for All Kids Assist until the child reaches age 19. If the 18 year old has a child, they may qualify for a separate TANF case.