Did you enter the child's Social Security benefits for 2018 on your tax return? Look at the Form 1040 Line 5a for total SS benefits entered. If there is no entry on Line 5a then the benefits were not entered. If the child's benefits were entered then you need to amend the 2018 tax return to remove the benefits.
A dependent child's Social Security benefits are never entered on your tax return. If the child has no other income they do not report the benefits received on a tax return.
See this TurboTax support FAQ for amending a 2018 tax return if necessary - https://ttlc.intuit.com/community/amending/help/how-do-i-amend-a-return-in-turbotax/01/27579
