What tax year is the upcoming Child Allowance based on? My son will be 18 this June and I dont want to get $3000 and then need to pay it back

[VolvoGirl]

New 2021 3rd Stimulus payment, Unemployment and Child Tax Credit (scroll way down)

https://ttlc.intuit.com/community/tax-topics/help/how-will-the-stimulus-package-impact-me/00/1393859

The new Child Tax Credit is for 2021, next year, when  you file 2021 tax.    It also raises the cut off age from 17 to 18 and makes the credit $3,600 for a child under age 6.

[Critter-3]

First the IRS knows how old your child is and will not be sending out the advance on purpose  BUT... whenever they get the portal open you can opt out of the payments in advance. 

.  More information will be available soon; the details of how it will be implemented have not yet been clarified fully.  There may be monthly payments going out beginning in July 2021, with some of the CTC still left as a refundable credit on your 2021 tax return next year.

https://ttlc.intuit.com/community/tax-topics/help/how-will-the-stimulus-package-impact-me/01/1393859...

https://www.irs.gov/credits-deductions/advance-child-tax-credit-payments-in-2021