You do not enter it on your tax return. Look at Box 2 of the SSA-1099 and you should see the child's SSN. If that is the only income a child has, then the child does not have to file or report it either.

Also see the following:

Do I need to report my dependent's SSA-1099 on my return?

https://ttlc.intuit.com/community/children-dependents/help/do-i-need-to-report-my-dependent-s-ssa-10...