I only have the base game, but I was having this exact same problem, and I'll tell you why...
Do you have any custom content loaded, specifically clothes? (Or have you downloaded Sims that may have come with custom clothing?)
From what I've read, this happens when cc is coded incorrectly, and you download it.
For example, in your case, you may have downloaded a shirt that was advertised as "for young adult women." But it wasn't coded right, so it's going on babies/toddlers!
(And when it does, it just warps the babies/toddlers into sticks, deformed figures, etc.)
Here's how to fix it....
Open your Sims 3 Launcher, and click on Installed Content.
Scroll thru and look for the following. If you find any of this, click "Uninstall" by each:
* New CAS Project (has a picture of a vampire woman on a t-shirt by it)
* Night time and day time every day shoes (picture of big lace-up boots)
* shymoo (Picture of a pink top/jeans. This is definitely a bad one from what I've seen)
* anything with .nkd by it (in my case, this was a set of black legs that said "bottom - nkd".)
* anything that says Metallica or metallic
* toddler_tee (mine had "milk" written on it)
- collectionblondes (Has a picture of a woman with a black bikini top and bottom.)
Hope this helps you! :)
I know how annoying it was to have this problem!!