@EmilieHak I've moved your post to the Sims 3 section.
The issue is likely one of your mods or sliders, even if there's no obvious suspect. You can test though in a clean game folder and isolate the culprit. Drag your entire TS3 game folder out of Documents\EA and onto your desktop. Open the launcher to create a new game folder, then test your mods and cc. Start with your .package files—you can copy the entire Mods folder from the old game folder to the new one, and then take half the files out. If Lisa Bunch (or whoever) looks normal in a new save, then the files you left in the new game folder are fine, and you can split the other group in half again and test those.
While testing, be sure to delete the five cache files in the new game folder each time you quit. They should be deleted every time you add or remove mods or cc anyway, and not clearing them may prevent some content, including the problem files, from loading properly, which could muddle the testing. For reference, the cache files are:
Keep splitting and testing until you've figured out which one(s) are the problem, remove them from your original game folder, delete the new game folder, and put the original back. (Delete your cache files before playing again.) If your teens still look abnormally tall, take them into Create a Sim, change some detail—it can be a hairstyle or a pair of shoes, it doesn't matter—and then see if they look normal. With some sliders, it's necessary to take a sim back into CAS to remove the effects.
If you don't have mods that make CAS available, you can access it via cheat. Bring up the cheats console (crtl-shift-c) and enter "testingcheatsenabled true" without quotes, then shift-click on the sim and select Edit in Create a Sim. Be sure to disable the cheat ("testingcheatsenabled false") when you're done.