Chill out folks! This question i geared to determine if children are eligible for bennies. Normally children get monthly bennies if they are under 18. They can get bennies up to 21 if they are full time college students. Apparently the law was amended to include kids over 18 who have not yet graduated high school. Apparently a few brats remain in HS a few months after reaching 18 based on when they were born and when they graduate, they might be 18 a month or two before graduating and should get bennies until they are out of High School just like their class mates not yet 18.
SSA law is complex and constantly changing mostly based on legal challenges and Congressional Hijinks.