If your 19 and 21 year old children are full-time students you can still get the $500 credit for other dependents for them. You do not get the child tax credit for a child older than 16. If they are not full-time students but they had less than $4700 of income of their own, you can claim them and get that same $500 credit for other dependents.
https://ttlc.intuit.com/questions/1900923-what-is-the-child-tax-credit
https://ttlc.intuit.com/turbotax-support/en-us/help-article/taxation/additional-child-tax-credit/L6x...
https://www.irs.gov/help/ita/does-my-childdependent-qualify-for-the-child-tax-credit-or-the-credit-f...
Additionally---if your children are full-time students, you should look into eligibility for education credits:
https://ttlc.intuit.com/questions/1901172-what-are-education-tax-credits
https://ttlc.intuit.com/questions/1901172-what-education-tax-credits-are-available
https://www.irs.gov/help/ita/am-i-eligible-to-claim-an-education-credit
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
