Well, since they're both hot, I mean, should have no problem...
Ok seriously. You can adopt, or you can steal-- I'll explain. If leaving the laptop in place of the stolen baby makes you feel better, you can do that too.
One of my sims "stole" her little sister after her mom moved out, (they all lived at the grandparent's house). I used the testingcheats code, took my sim over to mom's house, and shift clicked the baby sister/add to family. Then she took her home and raised her!
That's all I've got. Hope it helps.
--- "I am bi-gal, and I am right!" --bigalthesixth