Toddlers won’t age up sims 3

@Gabygav03  I would strongly suggest adding NRaas ErrorTrap and Overwatch for the overall health of your saves.  They work in the background cleaning up bad data and other errors that could otherwise lead to corruption.

To fix the issue itself, try adding MasterController, which does nothing at all unless you use it to issue a command.  You can then click on a toddler and select NRaas > MC > Stylist and change the toddlers' clothes and hair.  There's also an Edit in CAS option under Advanced, which you can try if Stylist doesn't help, but I don't think it's necessary to load CAS.

If this alone doesn't help, whether the game crashes or not, try reseting the affected sims, also under MC > Advanced.  This is a much deeper reset than the resetsim cheat: it rebuilds sims from the available data.

MC also has a Trigger Age Transition command, under Intermediate, but I'm not sure it would help here if the toddlers are actually disappearing from the portrait panel when aging up.  Still, you can try it.

If none of this helps, test without any of your custom content.  I understand you might not want to have to reapply all of your cc, but it would still be useful to know whether this helped.  Once you load the save with no cc, use MC to reset the toddlers again, "save as" and rename the save, then try to age up the toddlers.  If that doesn't work, quit without saving, delete the cache files, reload the save, and try again.  If removing the cc does help, but you don't want to get rid of everything, you can start testing the cc in the original save to see what you need to remove to fix the toddlers.