a dependent can not receive the credit. the fact you did not claim them is only relevant if you in fact were not entitled to claim them. if you are entitled to claim any of them then on their own returns they must mark that they could be claimed as a dependent
here are the rules for taxpayer's children
you are entitled to claim your child as a qualifying child if all these tests are met
• he/she has 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 under 19 at the end of the tax year. If a full-time student, he's under 24 at the end of the tax year.
• he/she hasn't provided over ½ his own support
• he/she didn't file a joint return unless there was no tax liability but merely filing joint 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 less than $4,300
• you provided over ½ his support
• he isn't a qualifying child of another taxpayer
