The world is good, bad and everything else in-between at the same time, and we try to stick to the good bits. I remember reading that children gain the ability to understand that around the age of 7. Prior to that, seeing the bad taints the whole world for them.

I can't tell if that's true, but intuitively rings so. Now, if it is of life-or-death importance to condition your children never to go into the forest alone while you are tilling the fields, perhaps that's a good tradeoff. Most medieval people died in their childhood anyway, worrying about their psychological baggage in adulthood was premature optimisation.

But in 21st century, I think we can do better, and wait with teaching children about the good and evil parts of the world until they are more ready for it.

That's not to say we dumb everything down and take away nuance. But it doesn't have to be gory. Bluey is full of nuance and suitable for all ages.