Have you been able to try with no mods or CC on a clean save?
When posting the original report I have tried on different, new saves, without and with mods. In both cases it wasn't working properly.
I tried again today and this time it seems to be working fine. I don't know if that was just a random one off issue, but so far it seems to be alright on a new save. It's just the one I am playing the most that has the most bugs. I guess it may be because I'm on my 12th generation and the save is just dying out.
Thank you for your help!
So the patch from 18/04/2023 is the one that fixed it.
My sim was then pregnant with the first baby, so she gave birth shortly after I updated with the patch.
The baby was born and grew up with the patch installed in my game.
The second baby was actually after the patch from 26/04/2023, it was born and grew up with both recent patches live in the game.
They both had the same mother (5 star celeb, beloved trait), and she was the one performing the "age up" with both babies.
