If you stir up the bedding and look really carefully, you will probably see tiny things moving. Those are the worms. The first time you get baby worms, it takes awhile, but the next time you transfer the beetles you will start seeing babies earlier because they are probably laying eggs as soon as you transfer them and also some tiny worms that you can't see might be stuck to them.
Baby mealworms take 6-8 weeks to become a good size.
I was sorting my beetles into another container yesterday and I noticed the oatmeal moving sorta like if you have grain mites. I am hoping those are baby mealworms and not grain mites! Also if you look on the moisture source (potatoe or whatever you use) I noticed an itty bitty mealworm baby on it. I was pretty excited. GOOD LUCK!