How do I find out who filed my child?

Wouldn't the Mother of your child, if she has custody, claim your child as a dependent on her taxes? If you called the IRS and explained to them, what you have not really explained here, perhaps they can help you.

See this (https://www.askmehelpdesk.com/taxes/someone-illegally-filed-child-21833.html). From our tax expert. Call the IRS to confirm who claimed him/her.