The ITIN has to be issued before the due date of the tax return for you to receive the Child Tax Credit in 2023. You can amend the 2023 tax return to add the child as a dependent but they would only be eligible for the Other Dependent Credit of $500.
See this TurboTax support FAQ amending a tax return that has already been filed - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-change-correct-return-a...
