Adoption psychology - own vs. alien

Loving and raising somebody else’s child as your own may take psychological preparation. We have all been brought up to distinguish between people and things as ours and alien. We claim our parents and expect them to favor us compared to others’ parents. We claim our friends, we claim our toys, our room, our house, everything we can tag as mine. And just by the virtue of calling it our own, we really do attach more affection to those people and things, don't we? Then how difficult could it be to call an innocent little child our own?