Superworms are what I used to feed my beardie, as well as a mixture of butterworms and waxworms for treats. Supers are very easy to keep - I bought a couple thousand online, purchased a tall plastic tub, three or four boxes of rolled oats, and viola! Pour the rolled oats in the container, pour the supers in the oats, and throw in a couple sliced potatoes for water (not too many as they will mold and kill your worms). As long as there are enough of them in the container, they won't pupate and turn into beetles.

The supers have a softer chitin than a mealworm and they move a lot more too, which entices your dragon to eat them. I remember my beardie loved them. You can get smaller ones for a baby beardie as well. A small note is that the supers CAN bite, so I always used non-latex gloves when I was digging through the oats for them.

Also, as they get older, it's better to mix in more greens, fruits and veggies for your dragons.