The general rule is not to feed any insect that is longer than the width of the chameleons head (eye to eye).
At this age they are going to be limited to crickets and maybe a couple of other small prey items. They are probably past the stage where fruitflies are of any use. You really can't start expanding the diet until they are quite a bit larger (IMHO).
Thanks for the past 2 days I have been trying to keep it in the low 70s using a heat lamp. My room temperature is about 68. So that means I don't need the lamp.