Per the IRS Instructions for Schedule 8812:

Taxpayer Identification Number Requirements

Each qualifying child must have the required social security number (SSN). If you have a qualifying child who does not have the required SSN, you cannot use the child to claim the ACTC on either your original or an amended 2019 return. The required SSN is one that is valid for employment and is issued before the due date of your 2019 return (including extensions).

You also cannot use a qualifying child without the required SSN to claim the child tax credit on either your original or an amended 2019 return. However if your qualifying child does not have the required SSN but has another type of taxpayer identification number issued on or before the due date of your 2019 return (including extensions), you may be able to claim the credit for other dependents for that child. See your tax return instructions for more information about claiming the credit for other dependents.

Therefore, if you enter an ITIN and select that the child is a lawful permanent resident (green card holder) or U.S. citizen, you will see a Yellow Alert titled Warning: Dependent Information.

If the child has an ITIN, but is eligible for an SSN: If you have not done so already, you should apply for a social security number for this child by filing Form SS-5 Application for a Social Security Card. Please see the additional information below. 

To enter or modify dependent information in your TaxAct return:

1. From within your TaxAct return (Online or Desktop), click Federal. On smaller devices, click the menu icon in the upper left-hand corner, then select Federal.
2. Click Basic Information in the Federal Quick Q&A Topics menu to expand the category and then click Dependents and other qualifying persons
3. Click Add to enter a new dependent, click Review to review dependent information already in the return, or check the box and click Delete to delete a dependent 
4. The program will proceed with the interview questions for you to enter or review the appropriate information

Additional Information

Applying for a social security number:

Form SS-5 Application for a Social Security Card from the Social Security Administration (SSA) is used to obtain a Social Security Number (SSN) or to change a name on a social security card. This form is available online, at your local Social Security Administration office, or by calling 1-800-772-1213.

The SSA Website provides the addresses of local offices.

Complete and attach Form SS-5 when you file the tax return for which the SSN is needed.

As the TaxAct® program requires a valid SSN to calculate certain credits and deductions, enter a "dummy" SSN of 899-99-9999 for individuals who do not yet have a SSN (i.e. a newborn child born in the tax year for which you are doing a return). Print the return and then white out the "dummy" SSN from anywhere it appears in the return before mailing it to the IRS. This ensures the return is calculated correctly for an individual that will be receiving a SSN. Attach Form SS-5 to the front of the tax return and on the first page of the return, write "Applied For SSN" in the whited out area. After Form SS-5 has been processed by the SSA, the IRS will assign a SSN to the return and process the return.

Alternatively, you can remove the child from the return, electronically file now and receive your refund. When you receive the Social Security Number you can amend your return, adding the dependent to your return to claim any additional refund.

For filing with some states it may be possible to paper file the state return in the same manner and send a copy of the federal return. The state will let you know if they need additional information or if they prefer you wait and file your state return after receiving the number from the IRS. You can check with your state Department of Revenue to verify their preference.