When doing this, there's no need to close the game. As long as you are in windowed mode and not in full-screen mode, anyway.

Pause the game, open the LDW folder, copy the family file to a new folder, unpause and try to make a baby (or whatever you're trying to do), pause the game again, switch to a different family, copy/paste the backup file back to the LDW folder, and switch back to your family.

Works just as well, and you don't have to sit through the loading.