You do not need a Social Security number for the child, but if you don't have one you have to have a birth certificate, death certificate, or hospital records showing that the child was born alive.
The following is from IRS Publication 501, page 22.
"If your child was born and died in 2023, and you don't have an SSN for the child, you may attach a copy of the child's birth certificate, death certificate, or hospital records instead. The document must show the child was born alive. If you do this, enter "DIED" in column (2) of the Dependents section of your Form 1040 or 1040-SR [in place of an SSN]."
