Yes, the Recovery Rebate Credit uses your 2021 tax situation, therefore when you claim another child on your return then you can qualify for an additional amount.
Please see from the IRS:
"Q E15. Dependents: Can my 2021 Recovery Rebate Credit include an amount for a qualifying dependent if the dependent received the third Economic Impact Payment or someone else received the third Economic Impact Payment for the dependent? (added January 13, 2022)
A15. Yes, if you meet the eligibility requirements to claim the 2021 Recovery Rebate Credit. The amount of your credit may include up to $1,400 for a qualifying dependent you are claiming on your 2021 return."
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