Make sure that the backup you saved was not overwritten by accident and that you have the right files backed up (if you're trying to make a baby in game slot 1, you need the files that have the number 1).. copy the backup files you made, and keep your actual LDW Virtual Families save files folder open for convenience.

Unpause the game and try for a baby, if it did not work out, pause the game again and switch out to another family. Keep this other family open, paste the backup files to replace the ones found in the save file folder and return to your other family.

Rinse and repeat from the unpause part, make sure you never overwrite your backups after you already tried for a baby Let me know if it still doesn't work for you Beth!