I agree with the babies comment. My current family keeps having unexpected children due to this bug. The wife gave birth, and I wanted to save her to my sim library. I went into manage neighborhoods, moved her out of the home and left her homeless. From there I saved her to the library, but noticed she was still pregnant. She had just given birth. I moved her back into the family, and the new baby was in the cradle. I did this again after she gave birth to the unexpected child, and the glitch happened again.
It wasn't just the births and pregnancy that were reset. The mother and father both took an age-away potion immediately after the birth, but they were old again when I returned from the manage worlds section. The parents and other sim children were reset to an earlier time before the birth, but the sim baby didn't get deleted. It's been born three times, and I have three different children. The three youngest children for a total of six.
I'm using mods, but the error seems the same as those already reported. Would you like a copy of this save file?
Info: All expansion packs and stuff additions
64 bit edition