Retired age 62.Child age 14 & rec'd 1/2 until age 16?she was full-time hs student.Now in college.Is $ retro when she was 16-18?

Retired age 62-now 71.Child was 14 when retired & she rec'd half benefit from 14-16. Thought is was suppose to be until age 18?She was full time hs student.Now in grad school.Wondering if SSI made mistake ending it at age 16?Can she get 2 lost yrs of benefits retroactive.My wife rec'd benefit also when child was age 14-16 while working part time but it ended when daughter turned 16. They ended both benefits when daughter reached 16. I think she as suppose to get it until age 18...is it retroactive