Interesting lore question I've been thinking about instead of finishing stories.
How much variation do you think there is between baby Pokemon of different species in regards to their state at birth and their growth rate (precocious vs altricial).
As far as we know, pokemon hatch individually (not from litters/clutches), which is generally a sign of high parental investment in nature.
In one story, KFC came out of the egg basically a fully functioning child, much like a real chicken. Do you think most Pokemon are born like that, or are they less common? Do you think they match up basically to their irl counterpart?
Personally, I like to think most species develop much like their irl species, but skewing more towards humanlike phases of infant/child/teen for the sake of relatability.
The game mechanic of "everyone hatches basically a full grown adult" is obviously a limitation on the gameplay and not to be taken as exact truth.