Mealworms pupating early

I recently went to buy some mealworms for my bearded dragon, but accidently bought babies instead of adults, which sucks but whatever. I problem lies in the fact that tons of these mealworms are pupating despite being babies. They're all kept together in one container and fed regularly, so I really have no idea why this is happening. So far, numerous pupas have emerged into beetles- all of them extremely tiny- but none of them have survived long enough for me to see them crawling around. They hatch completely, with no leftover shell stuck to them so I'm not sure why this is happening. What would cause them to pupate so young? Why aren't they surviving the process?