“Younglings” as a crappy word choice comes to you from the Star Wars prequels, specifically when everyone is horrified that Anakin killed “younglings.”
But, you say, look at that Star Wars Wikia pic you just posted. It’s meant to be used to refer to juveniles in a species-neutral way. It’s a piece of worldbuilding!
Maybe so. But, for one, you don’t need a different term for that. “Child” will work fine for the juveniles of sentients in general. Establish it by having characters refer to nonhuman children as children. Nobody will misunderstand.
Second, “he killed the younglings” sucks the emotional juice out of the scene, which is much more important than a small bit of superfluous linguistic worldbuilding. It comes across as a euphemism. Euphemisms exist to soften harsher words. And so “younglings” softens the impact of the idea that Anakin just slaughtered a classroom full of kids and reduces it to the impact of a nasty bit of vandalism. Oh, damn, we’ll have to repaint the whole nursery. What a shame.
And that IS a shame. If any scene should have high impact, it’s the scene that establishes that Anakin has gone full-on evil bastard. But letting a worldbuilding detail take precedence over the emotional impact of the story took the wind out of its sails.
Writers need to look to the integrity and purpose of their scenes and stories first. And that means killing children, not euphemistic “younglings.” When picking words, make the right choices. Your stories and your readers (watchers, for screenplays and their dialogue) will thank you.