Amending 2024 and 2023 taxes

I have been raising my grandchildren, paying for all of their care for the entire year for 2023 and 2024.  I do I find out if someone else claimed my 3 grandchildren?  How do I amend my 2023 taxes to include them.  Currently I don't have a social security number for my 2 year grandson and wasn't able to claim him on my 2024 taxes.  I hope to have his SS# in a couple months.  How do I amend my 2024 taxes to include him.