The father parent must file his state tax return separately.

IRS has nothing to do with that.

@Lisa7302008 

If he has a large state refund, he should wait until his back-due amount is updated.

There is no penalty for filing late for a refund.

@Lisa7302008 

Sorry, I meant his federal return, not state. Thank u

With such a large refund, his tax return is likely to be flagged for manual review. If that happens, it could be 6 months or more before it's processed. The IRS is severely backlogged this year, and anything that requires manual attention takes many months.