If they lived with you for the entire year, and their parent did not, then you would be the only one entitled to claim them. To claim a child as a qualifying child, they must live with your for more than 6 months out of the year. You would not be able to figure out if someone else claimed them without filing a return. If it is rejected for duplicate SSN then someone else probably claimed them. You would need to print and mail your 2023 return anyways, so you would end up getting a letter from the IRS asking for proof that they lived with you and not the other person who claimed them (IF someone else did)
Yes, when you get your 2 year old grandsons SSN you can amend your return to add him as a dependent.
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"
