It's in the game, but it's an optional sidequest with hidden collectibles scattered around all levels. The first picture is just a mockup cause we've sadly run out of time to make a proper cover for the game.
I played through the game again, trying to find everything, still didn't find even a single child. (I just noticed a white doll thing once, but that was unreachable). Are you sure that this sidequest is actually doable? I'm going to need some kind of guide on how to find them. Feels like there is some mechanic that I'm not aware of that I have to use to get to them