Dependent as a full time student

I have two children between 19 and 17, both are full time students.  TT allows me to identify one of them as a full time student, but not the other.  I’ve tried deleting the profile of the child that doesn’t get to be identified as a full time student and re-created their profile, but I still don’t get a chance to add them as a student.  Searched other threads on this topic with no luck.  any suggestions?  Thanks!