Kids in the 1950's didn't understand the importance of healthy eating.
For that matter, even most ADULTS back then didn't understand the importance of healthy eating.
I think the kid with the apple is being a typical kid, being jealous of the one with the candy bar.
Mother's milk has a lot of natural sugars in it, and so does infant formula.
We prefer whatever we are USED TO eating, so the younger someone is, the more they prefer things that have sugars in them.
This is totally natural.
But it is up to the parents to train their children to get used to things that are not sugary.
My daughter, now in her 40's, has thanked me more than once for not getting sugary breakfast cereals ... for having yogurt and carrot sticks always in the fridge for snacking. Because she never got caught up in sugary foods (even though as a child she really wanted them, and occasionally I would give her some).