Is it possible for someone with opthamalic shingles transfer chicken pox to a vaccinated child?

Unlikely to happen. There are a few vaccinated kids who remain less than fully protected, especially if they have not completed the two shot series. However, shingles is not as contagious as the wild chickenpox, it has no airborne phase. To be exposed the child would have to have direct contact with the material from the caretakers wounds. Simple hygienic care/handwashing/etc will avoid passing it on.