You do not select the Child Tax credit (CTC). If you are entitled to it, TurboTax (TT) will automatically give it to you.
If you think TT missed it (unlikely),
In TurboTax (TT), enter at:
Federal Taxes Tab (Personal for H&B version)
Deductions & Credits
-Scroll down to:
-You and your family
--Child and Other Dependent credit
