Child’s social

[Kellsb87]

What is my child social number 

[DoninGA]

Only you would have that information.

Look at the child's Social Security card.  Or look at a prior year tax return if the child was claimed as a dependent as the SS number will be on the tax return.

Or go to his Social Security Administration website for information on how get the child's SS card - https://faq.ssa.gov/en-US/Topic/article/KA-02723