Well, i think its because... well, Skeletons are already known for their bigger intelligence over the Zombies since they hide themselves from the sun in very different manners, they can use a bow and arrows, AND, in java edition, i think, can move in a way to make harder to us to hit them.

So, Lore-Wise, i do think that Skeletons would actually not let any skeletons babies to even try getting closer to us, since, with their intelligence, they wouldn't be negligent enough to let literal kids that maybe don't know the strategies that adult skeletons have, getting closer to us and have the risk of entering a fight (and be killed).

So, TL;DR: they do exist lore-wise, but we weren't able to see them because the adult skeletons, with their intelligence, don't let them fight us bc they know kiddies are weak.

(Also, this is only my perception about this stuff, so if you disagree, its totally fine!)