Where do I add ssa1099 on my children

You don't include their income on your return. It would only go on their return if they are required to file one.  If they only get ssi or SS, SSDI or a SSA-1099 they don't have to file a return and nobody reports it.

Filing requirements for a dependent

https://ttlc.intuit.com/community/children-dependents/help/do-i-need-to-file-my-own-taxes-if-i-m-a-dependent/00/26111

You do Not enter their Social Security benefits from their SSA-1099's on your tax return.  If the children have no other income they do not file a tax return.