Is there a way to age up an unplayed baby sim by cheat?

The easiest way to age up a baby, in this case, would be to go to manage world, and move (merge) the baby in with a family (or in with your sim if you are allowed or have the space), just make sure they have a baby bassinet set up in their home. Then take your sim to visit the family, and from there you can manually age up the baby. After your sim is finished visiting, and back home. you can go back to manage world and merge the newly aged toddler back with Morgyn.