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.

I don't know if you're opposed to using mods, but TwistedMexi has mods that allows you to set the age of Sims without leaving your household or having to place new ones down, etc..

This one has the set age cheat as part of it, but over all the mod unlocks a wide range of cheats that were taken away from us awhile ago: https://www.patreon.com/posts/cheat-fix-for-22697405

This one is just for setting the age, though it was last updated in Nov. 2018:
https://www.patreon.com/posts/cheat-fix-for-22697405

In either case, you'd open up the cheat menu and type in "tm.setage " and they should age up accordingly.

I have a situation where I created 2 households. I wanted a playmate for my child so each couple had a baby near the same time. Now I am finding it too complex to manage two households so I marked one household unplayed. Now I need to know if the unplayed baby will age up to toddler. I have aging turned off because I like children and don’t want them to age too fast. Will it work to just turn on aging for unplayed sims long enough for the baby to become a toddler after my active one does? I think I read that babies will age to toddler even if aging is off, at least for actively played ones. I also downloaded the Chinese new year family who has 2 toddlers. I am wondering if they will age to child.