I'm trying to do the "family" from Interview with a Vampire and [as odd as it sounds] I want Claudia [the little girl looking vampire who was like 150 years old] to BE an adult but look little. Not for any creepy reasons -- I just didn't want a deadly 150 year old vampire running around and playing patty-cake. I already have Louis and Lestat and a few of the others, but I want to make this work.

How do I change her age so she THINKS she's an adult but looks like a little girl?

And now I see how creepy this really sounds.

If you want to just message me privately or something that is fine too.

Well, it does sound creepy. The PM request does unintentionally add to the creepiness. I guess you could just have her a YA, make her really thin and underdeveloped, and get some decent Lolita type clothing for her, all of which might get you close to the "look" you want but also sounds creepy. Good luck.

Bear in mind that in TS3 children cannot perform most adult interactions, because children require completely separate animations for every interaction they perform. So even with intensive modding, you are really going to have no luck getting a child-model Sim to act like an adult, unless you're prepared to provide dozens of new child animations, which a lot of folks would be very grateful for

By playing with the custom sliders that are available, though, particularly the height slider, you may be able to make an adult sim look (relatively) child-like.