Could be a couple of things.  Have you fully gone through the Child Tax Credit menu in the Deductions and Credits section?  When you went through the dependent screens, does your child show up as a DEPENDENT?   Did you report at least $2500 in earned income?   To qualify for the Child Tax Credit, your child must fit all of these requirements:

• Be under age 17 at the end of the tax year - this means they have to be 16 or younger as of Dec. 31, 2020.  
• Is your son, daughter, stepchild, foster child, adopted child, brother, sister, stepbrother, stepsister, half-brother, half-sister, or a descendant of any of them (for example, a grandchild, niece, or nephew)
• Has his or her own Social Security Number
  • Children with ITINs don't qualify, but may instead be eligible for the $500 Credit for Other Dependents
• Lived with you for more than half the year
• Didn't support him/herself (didn't pay more than half their own expenses)
• Is a U.S. citizen, U.S. national, or U.S. resident alien
  • Residents of Canada or Mexico wouldn't qualify

Up to $1,400 of the credit is refundable and is phased-in based on your earned income.  In most cases, you must have $2,500 or more of earned income to be eligible for any portion of the refundable Child Tax Credit.

The $2,000 per-child credit is reduced once your AGI reaches $200,000 (or $400,000 if you're filing jointly with your spouse).

I went through it twice.  Income is enough and well under the 400K for married file joint.

Ok ... so let's take a look at the form 1040 ... on the dependent line box 4 ... which box is checked ?   CTC or Other ?

If it is the CTC then review the form 8812 and the 8812 worksheet to see how the credit is being calcualted.

How do I preview my TurboTax Online return before filing?

You can view your entire return or just your 1040 form before you e-file:

1. Open or continue your return.
2. Select Tax Tools in the left menu (if you don't see this, select the menu icon in the upper-left corner).
3. With the Tax Tools menu open, you can then:
   • Select Print Center and then Print, Save, or Preview This Year's Return to preview your entire return, including all forms and worksheets (you may be asked to register or pay first).
   • View only your 1040 form by selecting Tools. Next, select View Tax Summary in the pop-up, then Preview my 1040 in the left menu.

Related Information:

• Why does my return say "Preview Only"?

Other has an X in it.  why?

How do I change it?