If the child's only income is on a SSA-1099 (survivors benefit, I assume), then it is not taxable and they do not have to file a return. If the child has other income from working or from investments, the social security income might be partially taxable. You would prepare a return in the child's name and let Turbotax tell you if any tax is owed. (If using Turbotax online, each tax return requires a different account with a different user name and password.)
Turbotax may not be able to prepare a free return if the child has taxable income. You may want to look at one of the other IRS FreeFile options.
https://www.irs.gov/filing/free-file-do-your-federal-taxes-for-free
