Beginning with tax year 2018, if you, your spouse or dependent child did not have a Social Security Number by the due date of the return (to include extensions), you cannot claim the Child Tax Credit, Additional Child Tax Credit or American Opportunity Credit on either your original or amended return. This is true even if you later get an ITIN or SSN.
If the dependent does not have a Social Security Number but does have an ITIN (Individual Taxpayer Identification Number), you may still qualify to claim the credit for Other Dependents (up to $500) on your tax return.