To be considered a 2024 gift, the transfer of the money to the child has to be completed by December 31. But you can give a gift under the gift tax exclusion every year. If you don't make the gift by December 31 you can make it a 2025 gift.
The annual gift tax exclusion for 2024 is $18,000 per person. For 2025 it's $19,000.
