Are you saying that you didn't add all of your children on your tax return or that you only claimed one as your eligible dependent? Only one child can be an eligible dependent; it is a credit that you would have had if you had a spouse. If you made a mistake and never added a child, then you can simply go to the CRA My Account and fix it there. We recommend that you contact the CRA at 1 (800) 959-8281 to advise them.
Thank you for choosing TurboTax.