It
depends. Usually, the Child Support has a precedence and the IRS
will take his refund (the amount he owes) to cover it. In certain
situations the IRS can release the refund for the child support, but it will
not happen automatically.
Here's a link to the Treasury
Offset Program with more information: https://www.treasury.gov/services/report-fwa/Pages/treasury_offset_program.aspx
