If the child is a student, the age limit is different. TurboTax knows: "be under age 19, or under age 24 and a full-time student for at least five months of the year" and you can google:

irs child tax credit for college students

child is 18 and student in highschool  but need answer yes or no for 23 and 24

You posted this under Practice Advice.

It helps to post the topic into the subforum for the program you are using, and give some details to describe which form and year you are working on, such as ProSeries (basic) and 1040 2021.