Typically, most species start feeding at second instar (or third instar, if you count post embryos as first instar). A few species start feeding at third instar (or fourth, again, if you count post embryos as first instar). Despite this, they do cannibalize as early as post embryo/eggs-with-legs/first instar.
Anyway, when the six-a-six-ies are ready to feed, you'd feed them pinhead crickets/roaches, baby mealworms, fruit flies, or you can cut up larger feeders into appropriate sizes. Some have even fed fish food!