My fiancee and I got into a discussion with her parents on NFP which then got on a tangent where we disagreed with her parents. Her mom made the statement that "God wills all children" so I asked "What about the children of rape and fornication? Was it God's will that they come into existence? If so, are you saying God used fornication/rape/sin in His will to bring about a life?" Her mom though that God completely willed those children throughout the entire sexual act even in the instances of sin but wouldn't agree that it meant God was willing sin, which He can't do.
My fiancee argued (and I agreed with) that God has bound Himself to nature in that if two people have sex, regardless of the morality of that sexual encounter, and nature works as planned then God will infuse a soul into that child because He has bound Himself to do so in the way He designed nature and sexual intercourse. We agrued God is only involved in the conception of children from rape/fornication in that He infuses the soul and co-creates with that couple, although He did not will that a child be born because then the child would be a result of sin so God would have to use sin in His plans.
We of course emphasized that God can bring about good in all circumstances and that God loves that child very much, but that He did not actually will that child to come into being since his/her's coming into being involved sin.
Her parents agrued that if God did not will for that child to be born via rape/fornication then He would not allow the sperm to get to the egg, or would have intervened in some super natural way to prevent the pregnancy. According to her parents if God does not prevent a pregnancy, then that means He willed the child to be conceived.
I hope this makes sense, please ask me to clarify something that doesn't. To conclude, if my fiancee and I are wrong please correct us. If we are right, or mostly right, please help us with more solid reasoning and particularly writings from the Church or well respected theologians to back us up - her mom asked for some documentation as it is the only way we could change what she "feels in her heart is right." Also, feel free to provide evidence on why we're wrong on the very slight chance that we are.
Lastly, her parents had difficulty thinking that God has bound Himself to anything. I pointed to the meaning of a covenant and various examples in the Old Testament but they weren't really convinced. Any direct passages from Scripture or other Catholic sources on God binding Himself to people/things would be helpful. Also, if
God has bound Himself to infuse a soul if two people have intercourse and nature takes it course would you please provide any documentation you know of concerning that? That God will infuse a soul into a child at conception even if He did not will the child because the sexual act was sinful? We of course may be wrong as we were just trying to follow things logically, but we think it makes sense.