I had twins get IF dolls. Both played with them as toddlers. When one became a child, I took her IF out, and he grew up, too. When the other grew up, I took out her toy, and it vanished. But now she still plays with it, only it's invisible, even when I've clicked on her. It doesn't show up in her inventory either. I saw on the thread that someone else had this happen, and am curious what happens with the totally invisible IF -- does it ever become real? does the teen interact with it?
EDIT -- Okay, the invisible IF became visible when its Sim became a teenager. It's still a doll, but it can change positions like a gnome. I don't know yet whether it can move somewhere else. Also, the twin with the regular IF would play with the invisible one when her IF was out and running around.