I was just thinking for the character screen like just three generic body type renders, not like doing some overhaul just for weight gain fetishism including the sex scene images, just something to mess with. I'd much rather being able to influence the growth of the kids.
Well-fed and training skills up = taller more adept physically, boys end with a stronger body, girls also taller "full" body in a generically attractive sense (curvy/full thighs/etc in a 80%+ agree she's attractive kind of way) where it rewards MC for focusing on their development. A little side thing that has good rewards for MC essentially having two very strong late game characters for putting in the time on them as they get them would be a cool thing.
Maybe if you hit a certain threshold with raising them, they're characters who can break the 100 skill cap (playing into the aspect of MC isnt necessarily the "peak" of human capability, but you can make the kids that way would also be a nice touch).
Especially if fighting the overseers/bosses of the world, or a war on planet is part of the plot later on would be cool to have that as a way to improve your fighting power. Currently it seems like fighting the big monster at that river outpost is more or less the current build's "hidden boss?"