There are easily researched major developmental milestones, such as the capability to understand that objects exist when you’re not looking at them. Describing a world that does & doesn’t have certain realities could be very interesting. Parents are often shocked by the presence & absence of certain abilities in very young children. For example, preschool kids are wired to memorize large amounts of information very quickly without making decisions, so they’re really good at large scale rote memorization tasks. (Just go to YouTube & search for videos where children recite all of the countries in the world, all the chemical elements, or more obscure topics.) What they can’t do is perform a task based on anything more than reciting the list. They know they learned “Germany” but they didn’t learn what another country is; not just what “Germany” is, what the concept of another country is. Memorizing the words isn’t the same as knowing the thing’s qualia.
Let’s say you make them learn how to make coffee. They can probably do this task, but they don’t have understanding of what coffee is - even if you tell them & they say the answer back to you - because they only know there’s this box that will make the water change color. The fleshing out of definitions for all of these things is a process that requires years.
Which brings me to the other side of child-stats: Impossible tasks.
They can learn to play piano. They can learn to make coffee. They can do things like this from a very young age. Putting aside literally impossible tasks due to their body (such as some things related to taste, for example), there are a lot of cognitive tasks that require a part of the brain that literally hasn’t grown yet. One of my favorite examples of this is the difference between ethical vs. moral behavior. They can’t navigate complex moral tasks. To do so they have to understand more than the intuitive pre-wired “don’t make someone bleed” instinct. They actually have to be able to use their mirror neurons to put themselves into someone else’s shoes, then imagine how they themselves would act under different stimuli, & that requires recall of countless cultural rules as well as personal experiences. I’m not even talking about hormonal stuff here, as most children understand that humans feel love. They can’t understand human behavior that’s motivated by unnatural influences such as money & cultural taboos. These things aren’t pre-wired by genetics. If you want to really write a story from a kid’s perspective, force a teacher to explain to the kid why the kid’s bully isn’t being punished. (A violation of two innate expectations: We’re wired for both empathy & to expect defense by the adults around us.) No matter what happens, the kid will probably interpret the adult’s explanation as a punishment of the victim. How they twist that punishment out of the adult’s words will be very different based on how their mind can process what the adult says. Tell the same story from the perspective of the same kid just two years later. No matter how old the kids were, if the first example is at least about age five, any accurate first representation will be wildly different from a second example that’s at least two years later. Refuse to punish the kid’s bullies often enough, or with a severe enough incident at the right age, & you can also do some serious damage during their development. You can wind up with the kid either being extremely anti-bully, a bully themselves, a cop, a teacher, obsessed with parent’s organizations that want to censor stuff, or a violent vigilante based on when the incident happens & how much of an impact you make.
Maybe just go to Wikipedia, look into childhood development there, see what ideas strike your fancy, & do some more research using child psychology textbooks. This is a deep topic.
