you don't have to claim your son if he qualifies as your dependent. however, if he can be claimed as a dependent he must check that box on his return even if not claimed. the IRS may catch the Social Security omission during its review process and send you a notice. TurboTax says it will not have the amended return form - 1040-X - ready until 3/25.
you can claim him/her as a qualifying child if all these tests are met
• he/she had the same principal abode as you for more than ½ the tax year. Temporary absences like for school are ignored
• if he/she is not a full-time student, he's/she’s under 19 at the end of the tax year. If a full-time student, he's/she’s under 24 at the end of the tax year.
• he/she hasn't provided over ½ his/her own support
• he/she didn't file a joint return unless there was no tax liability but merely filing jointly to facilitate refund of taxes withheld or estimates paid
or you can claim him/her as a qualifying relative if all these tests are met
• his/her gross income for 2020 was less than $4,300
• you provided over ½ his/her support
• he/she isn't a qualifying child of another taxpayer
