Social security number (SSN) required for child tax credit. Your child must have an SSN issued before the due date of your 2018 return (including extensions) to be claimed as a qualifying child for the child tax credit or additional child tax credit. If your dependent child has an ITIN, but not an SSN, issued before the due date of your 2018 return (including extensions), you may be able to claim the new credit for other dependents for that child.
https://www.irs.gov/individuals/steps-to-take-now-to-get-a-jump-on-next-years-taxes
