Newly hatched dragons are still full of yolk from the egg. Typically they won't start eating till 2-4 days after hatching. It is fine to offer some crickets (no bigger than the space between their eyes) a couple days after. If they are hungry they will eat them, if not they will just ignore the crickets. Remove any uneaten crickets as these can prey upon your dragons during the night.
Once they do start eating, feed hatchlings as any crickets as they can eat in a 10 min period, 3-4 times a day. Pinhead to 1/8th of an inch size crickets are usually fine for baby dragons. You can also leave a bowl of finely chopped greens in the cage all day, but hatchlings probably won't show any notice of them, but some may nibble on greens.
Don't forget to dust crickets at least twice a day with calcium, they grow so fast at this age, they need the extra calcium.
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PHLdyPayne