It appears they are all being treated as being eligible for the Family Tax Credit of $500.
You are correct, that only children under 17 will be eligible for the Child Tax Credit and Additional Child Tax Credit. You may need to check your input and verify that their birthdates are entered and that it is indicated that no one else can claim them.
To check the requirements, see: Child tax credit by the numbers | Internal Revenue Service
Child Tax Credit - TurboTax Tax Tips & Videos
