Sims 2 Legacy bug Toddler stuck thinking it's a baby

I have the same problem as well. I happen to have my 3 children grow up in the same day (1 goes to teen, and the other 2 go to toddler) Everything works fine until I exit the game WITHOUT SAVING. Then, I play this family again and find out that all of their body and their age are stuck in their previous stage, but they all have their upper part of the body of their older stage (1 have teen's head with kid's body, the other 2 have toddler's head with baby's body). The teen with kid's body can finally be fixed because I can manually age him up himself to be teen again. Sadly, for the toddler, they cannot age themselves without someone carrying them and the game doesn't allow other sims to carry them (I don't know why) and so it stucks with the error message like you

I play so many hours with this family and now it's unplayable. I'm so upset with you EA. So much glitches with this game.

I just had this issue myself & I have no clue how to fix it without using SimPE. If you have SimPE, it's an easy fix. BACK UP YOUR HOOD BEFORE DOING THIS! (And I don't promise this won't lead to issues down the road! But doing this fixed the issue instantly for me & I haven't noticed any adverse effects.)

Open the hood containing the boddler (baby toddler) using Neighborhood Browser, then use Sim Browser & find your sim that's stuck, click on them & open their profile, then change their age in the bottom panel from baby to toddler. Once you open your game again everything should be fine. As a precaution, I also cleared my cache (groups.cache & accessory.cache files) & deleted the Neighborhood Manager file before reopening the game (these files can be safely deleted, the game will regenerate them as needed).

If you don't have/don't know how to use SimPE, I don't know of any other fixes, sorry. Resetting the affected sim using moveobjects is said to work, but that did nothing for me. Googling "Sims 2 Boddler Bug" may yield some alternative solutions.