I have this issue too, but it's happening with a child female sim and not a toddler, when I use cheats to trigger transition, she just shakes the birthday shaker and then walks off, it was working before because she aged from a toddler to a child just fine, and previous games I was playing the children aged just fine, I did install a couple of new outfits and items recently so that might have caused it but I always check with Custard before installing anything and Dashboard afterwards, I haven't tried another family yet, so that's the next step I will try, I'm also uninstalling some of the files I installed just shortly before this happened but while it was still working.