child tax credit

To claim a child for purposes of the Child Tax Credit, they must either be your son, daughter, stepchild, foster child, brother, sister, stepbrother, stepsister or a descendant of any of these individuals, which includes your grandchild, niece or nephew. An adopted child is always treated as your own child. An adopted child includes a child lawfully placed with you for legal adoption.

If the adopted children meet the above criteria they are claimed as your child on the tax return and not other dependents.

You should click the box that says "child tax credit" instead of "credit for other dependents" on your From 1040SR first page.

You can amend the 2020 tax return to claim the child tax credit. 

https://ttlc.intuit.com/community/amending/help/how-do-i-amend-my-return/00/27439 

If you filed your tax return using some other provider or self then also turbo tax can help you file an amended return.