From the IRS.GOV
Important changes to the Child Tax Credit will help many families get advance payments of the Child Tax Credit.
The IRS will pay half the total credit amount in advance monthly payments. You will claim the other half when you file your 2021 income tax return. First advance payment on July 15, 2021.
You may would like to remember that when you file your 2021 taxes, your refund may be smaller because you would have already received most of your child tax credit.