The IRS does not ask for proof that a child lived with you more than 6 months. If you choose to claim the child as a qualifying child on your tax return, no proof is needed when you file your tax return that the child meets the requirements to be claimed by you. The only time it would possibly come up is if someone else also claimed the same child. Then the IRS would ask for documentation for each person that claimed the child showing that the child met the tests to be claimed by them. This usually doesn't happen for many months after the tax return is filed.