I agree with all above comments.
Children would play no significant role as far as gameplay goes. They would be about as relevant as weaving a basket (using mcmanusaur's example) in regard to gameplay.
Certainly there are circumstances/games where Children play a significant or relevant role, such as in The Witcher (1). Of course, such roles often solely relate to the RPG/story aspects, and have nothing to do with combat.
Consequently, if Sui Generis is to have a primary focus on combat gameplay mechanics, then it is understandable why they would want to leave Children out of it. If they had enough funding to (and wanted to) create a AAA-type game with theatrical cutscenes, where a linear story was the main drive behind the game, then it might be more relevant to include Children. If relevant to the story/atmosphere, as in The Witcher. Note also that Children were unrealistically invincible in The Witcher, which was appropriate but reduced immersion.
However, in a less linear-story-driven game with a non-linear open world, I agree with Tony that the relevance of Children does become diminished. Great if it's there... but less important. Take Skyrim, for example. The ability to "have Children" just seemed stupid and out of place, IMO.
Ultimately, I think BM have already weighed it up shrewdly.