In The Sims 3 for the PC, you can have a ghost baby in your family.
First you’ll need a sim with a trait of Kleptomaniac so you can steal things, and a female sim with the Fertility Treatment award.
Make your Kleptomaniac sim visit the graveyard and steal male remains, and place them in your home. This will make a ghost appear in your house from 11pm to 4am every other night.
Have your female Fertility sim interact with this ghost sim just like any other, and try to woo them. Once you get them to Best Friend status, they’ll visit every night. Keep trying until you can get a woohoo with them, and your sim will eventually get pregnant, and you’ll have your ghost baby.