Well, I probably won't make mechanics on that, but the story will cover raising children. However, the story mainly revolves around the MC expanding the farm while avoiding the authorities, and his relationship with the girls he captured. Story-wise, certainly he will impregnate his daughters when they are at the legal age, because he doesn't believe incest is wrong. On the contrary, he is more attracted to his mother and sisters exactly because they are close to him. There has to be a huge time-skip between his daughters getting born and getting to the legal age. In a realistic situation, if you look at most of the father-daughter incest cases in real life, the father often violates the daughter when she is underage, but writing that in a story brings lots of problems so, I'm not going to do that.
I have considered about making mechanics in this game, but that would require turning this into sandbox, which I'm not a fan of. But I have considered mechanics such as keeping track of the milk produced by every girl, selling milk for money, and using the money to in turn expand his farm and shops, cum reserves, and so on. But, it'd be a completely different game. So, sorry about this, but just use your imagination that these factors are driving the story. Things like these are mentioned in different parts of the story.