I claimed my boyfriends two girls on my taxes bc he hasn't worked in a few years. Didn't get stimulus for them. Do I need to amend so he can get the pymts?

Not, if you act now.  In order to get the child Recovery Rebate Credit the child must qualify for the Child Tax Credit.  Since the children are not related to you they would not qualify.  However, they would qualify as his dependents (see criteria below).

If you have already filed, you have a unique one-time opportunity to make a correction to your 2020 return without amending.  Use this link to have your tax return sent back to you before 6 February.  Make the corrections and resubmit.

 The child qualifies you for the CTC if the child meets all of the following conditions.

1. The child is your son, daughter, stepchild, eligible foster child, brother, sister, stepbrother, stepsister, half brother, half sister, or a descendant of any of them (for example, your grandchild, niece, or nephew).

2. The child was under age 17 at the end of 2020.

3. The child did not provide over half of his or her own support for 2020.

4. The child lived with you for more than half of 2020 (see Exceptions to time lived with you , later).

5. The child is claimed as a dependent on your return. See Pub. 501 for more information about claiming someone as a dependent.

6. The child does not file a joint return for the year (or files it only to claim a refund of withheld income tax or estimated tax paid).

7. The child was a U.S. citizen, U.S. national, or U.S. resident alien. For more information, see Pub. 519, U.S. Tax Guide for Aliens. If the child was adopted, see Adopted child , later.