Ideas
I can reproduce this on my PC & Xbox.
EDIT: I have an update, maybe a work around
1. Ctrl+Shift+C -> CAS.fulleditmode
2. Load into CAS -> age Child up to Elder -> return to LiveMode
3. Load into CAS -> age Elder back down to Child -> Return to LiveMode
4, Child no longer appears pregnant
I can't say this is a solution but it looks promising.
I have two child Sims created on PS4 somewhere in 2019. Those Sims (2 separate families) were uploaded to the gallery from PS4 in 2020. I created a PC save in 2021 converting those 2 Sims to Base Game as I was moving from PS4 to PC. One of the female child Sims was an alien but lost that status as they were converted to a human Sim at that time. I still have my 1st save created on PC in 2021. Loading into it today I found these 2 female child Sims appear pregnant in the Base Game save on PC. I eventually bought packs back and now have a PC save with the original PS4 Sims on my PC. In my current save they also appear pregnant.
Curious, I loaded into my Xbox Series X to an existing save on that console & found yes, these 2 Sims also appear pregnant on Xbox.
I have the saves uploaded to my Google Drive as well as screenshots. I will be sending them to Cade as requested. Images below are Xbox & PC.
These are the Gallery Listings for the families. I have left the description so they can be found by hashtags if they do not appear in a search through the household names. Both of my gallery's are pretty long.
These are from PC in today's save. Same Family.
The issue is reproducible by downloading these families to a New Save game on both PC & Xbox. I have another household as well but didn't want to flood the feed with 20 pictures. I already think this is probably too many.