After saving my game, installing some new content, and loading I noticed the thumbnail for my child Sim wasn’t selectable. I read up on resetting Sims so I did that for the butler and saved and went back in. The child Sim completely disappeared. I freaked out and tried finding a solution but found none. She appeared in the family tree but wasn’t visible in game or as a thumbnail icon. I had a last-ditch idea to save her…
I took the family to China. They all loaded up in China and are all selectable.
However, when I got back home the child Sim was gone again. The only thing I was able to do was export just the family (eviction locked up the game). I deleted all saved games, loaded up a new map, and put the family back. That’s the only thing that worked.