If you told the Marketplace your children would NOT be your dependents, they SHOULD have sent the child his/her own separate 1095-A, and they would calculate their own credit on their own tax return. If they did not do that, there is probably nothing you can do (and it might end up being a good thing).
If your child IS your dependent, then yes, their income is included in the calculation of the credit on your tax return *IF* their income was high enough that they were required to file a tax return due to having "taxable income".
