The father is my sim, living in the house that I am playing. He invites her over to his house for a date, and they "Try for Baby." A few days later, he either gets a call saying that the baby was born or the baby just shows up in his list of relationships as a friend.
The mother is a sim that he met wandering around town, and she does not have a house in any neighborhood. Once she gives birth, the baby is in my sim's list of the relationships, but the mother has disappeared.
When I go to Manage Worlds, then Household Management, and look under Unplayed Households, there is a household listed under the last name of the mother and new baby, but the photo is just blank. If I try to move the household into a home, it says that I can't because there are no adults. It often crashes the game as well.
Finally, I discovered that I could move this "invisible" household in with another family, and just the baby would move in.
Now I have a couple raising my sim's 4 children, born outside his home to 3 different mothers, since their mothers "took off." haha
I even did this with the maid once. She gave birth to my sim's child, and then we got a new maid. She was gone.
Any ideas?