without being able to see your return or what info you entered for the children we can't say why the IRS denied the credit. was a reason given?
if all the children are qualified (under 17 on 12/31/2020, US citizen or resident alien, has a valid SSN for employment) you would have a tax liability that would be eliminated by the regular child tax credit. then if your AGI is earned income (wages or self-employment income) you should have gotten an earned income credit which is refundable. there would also be the additional child tax credit which is also refundable. to get the additional CTC form 8812 must be included with your return.
if you believe you qualify based on the above you should contact support because you can allow a Turbotax pro to actually see your return to determine what the issue may be
Contact Customer Service
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https://support.turbotax.intuit.com/contact
800-446-8848
