random baby in relationships, wont delete

Newborns are objects and cannot be edited in CAS - you could wait until they age up to infant (or go age them up early), or you could try going into build mode on the father’s lot to delete them. Not sure if the second option will work or what happens if the game thinks they have a baby and you’ve deleted the baby in build as I never tried that way.

As for how/why they’ve suddenly had a baby… I don’t know. It doesn’t seem like it should be possible - you say your played Sim is the mother? Did you have her (or anyone) discuss expanding the family with the father?

This just happened to me. I clicked the mailbox and it brought up mc cheats. Under the menu there is deletion cheats. Click that and delete by age. I deleted all babies and this worked. If you play multiple households and have a baby that you would like to save, keep in mind that the baby will be deleted. You must have MCCC for this to work and you can always delete the mod after you have saved and it has served it's purpose. I hope this helps.