No, a deceased individual cannot make a gift, the deceased individual's estate cannot make a gift (the deceased individual's will would have to have named the child's 529 plan as a beneficiary, in which case it's not a gift) and it's not permitted for you to make a split gift after the death of your spouse. If you make a 529 contribution of more than $15,000 in 2019 you must file 2019 Form 709.
