I misread your post to read that they were getting a W-2 in which case there would be no reporting requirement. Otherwise they would have to report the income as self employed on Sch C and pay self employment tax as others have indicated.
Technically you don’t have to report that income to fund a Roth but to avoid any letter of inquiry from the IRS it wouldn’t hurt to use one of the many free file programs to file a return anyway
