Removing babies from Genealogy

There isn’t a way to delete a Sim from the family tree. If your family tree starts at the parents you could save your current family of 3 to your library, delete your old one, then place a new copy back in your save. It will lose other relationships but get rid of the baby in the tree. There are mods that can be used to quickly restore relationships if you don’t want to build them back up (or for relatives they may have had).