How old are they? The child has to be UNDER 17 on Dec 31. And you need at least $2500 of income from working to get the CTC or the additional child tax credit.
And see this rules here, What is the Child Tax Credit
https://ttlc.intuit.com/turbotax-support/en-us/help-article/taxation/child-tax-credit/L2lNhfGDl_US_e...
