Is it from Social Security on a SSA-1099 form? 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 got Social Security or SSDI or ssi 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-d...
