Well, it would have been too late for me I guess (laugh). I don't know, I don't like treating children in such a disrespectful way. From what I have seen about children they are just little people in little bodies and they have a capacity to understand things that adults often don't. So, in my opinion, a lot of these education theories are made by adults looking down on children.
One of the stories that I remember a lot in the scriptures is about the Buddha as a child being taken out to see the plowing of the fields. The adults were oblivious to the suffering of the ox, as it was working and sweating. They were oblivious to the suffering of the earthworms being chopped in half, and the beings being buried. But not the Buddha as a child. He opened with Compassion to that scene and actually this was his first recorded spiritual experience of that lifetime.
When you look at fairy tales, there is a lot of "doom" and wrong views, so perhaps it might be better to give them a little bit more "doom and gloom" with a few Right Views mixed in with it along with other things.
It really depends on how you approach the subject of Dukkha with children and how wise the teachers/parents are. Perhaps with the current materialism in the world, it may be just an effort to pass on the adults' wrong views of wishing for happiness in the world.
Why I said it was too late for me: I remember quite a few times when my pets died or ran away and all these sort of things. And where I think my parents were talking about being eaten by sharks and how to deal with that, all these sort of things. In Australia, if you don't talk about death, you may die sooner than necessary! I was very happy actually when my father taught me what to do if I ever got caught in an ocean riptide, because it happened when I was eleven. It was quite frightening, but my father had talked about the possibility of that, so I followed his advice and managed to save myself.
Understanding the possibilities of Dukkha arising helps us to deal with it. I have also seen parents talk about things like death to small children and their capacity to understand. I would say as far as "doom and gloom" goes, if it's to expose the child to particularly negative, immoral sort of attitudes in the world, yes, I would agree with that, but not the laws of existence.