Only if they lived with you prior to the adoption for a combined total of MORE than 6 months and you can claim them as a dependent on your return. If one of them came to live with you at birth and continued to live with you, you can count that as the whole year, even if they were not born prior to July.

In order to claim a child as a qualifying child for the Child Tax Credit they must have lived with you for more than half of the year and meet a few more criteria below.

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

1. 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, you grandchild, niece, or nephew).
2. Was under age 17 at the end of 2018.
3. They did not provide over half of his or her own support for 2018.
4. They lived with you for more than half of 2018
5. They are claimed as a dependent on your return.
6. They do 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. Was a U.S. citizen, U.S. national, or U.S. resident alien.

https://www.irs.gov/publications/p972