Oomis,
Would raising children as if they were ones own not fulfill the mitzva of having children if it is clear that one cannot conceive naturally? (and that means without fertility treatments)
Must a child be born from ones own body for it to be considered ones own? “
You are asking two separate and very disparate questions. I will deal with the second one first. OF COURSE a child who is adopted and loved by a non-biological parent, is that person’s child. There are parents by nature and there are also parents solely by nurture, and they are every bit as choshuv as the other.
If the mitzvah of pru urvu which is incumbent on all men, is met by raising adopted children, then I defer to your greater knowledge. But my logic (and yes, it may be faulty and also ignorant of the halacha)tells me that just as a Yisroel cannot be a Kohein, no matter how much he wants to be a Kohein, no matter how truly ehrliche and sincere he is in his avodas Hashem, he nonetheless cannot fulfill the mitzvos of a Kohein unless he in fact is a Kohein.
If a man has not sired children, he has not been fruitful and multiplied. He may have a host of other mitzvos and earn incredible s’char mitzvah in raising a child he did not sire, but he and his wife have noentheless not brought children into the world, and there is a sadness in that. I think adoptive parents are awesome baalei chessed. But I doubt that any one of them would not do just about anything to be able to give birth to a healthy child.