What disallowed or reduced credits are reported on Form 8862?

If you had the Earned Income Credit, Child Tax Credit, Additional Child Tax Credit, Credit for Other Dependents, or American Opportunity Credit disallowed or reduced on a prior tax return, you may need to file Form 8862 to claim the credit again.

If the IRS reduced or disallowed a credit, they should send you a notice to let you know why it was disallowed and to tell you that you need to file Form 8862.