when you say Parent do you mean “in the existing level/blueprint hierarchy” (the technical term for this is composition) or “Parent Class that it is derived from” (this is called inheritance)
for the first situation (Composition) you need to get the specific instance of the container to the data for the specific data member variable to be in scope.
for the second situation (inheritance) the Parent class has no knowledge/understanding of what the derived classes add, or modify (those kids always adding new variables and not telling their parents about it) while to get to those members added in the derived class would require casting to that type.