Sure, mealworms and other insects are fine. Just match the sizes to the chicks (i.e. don't give gigantic bugs that might be unable to move out of ithe crop). I gave flightless fruit flies to my 1 week olds, and as they grew added 1/4" crickets, small mealworms, and about 3 weeks old I started using waxworms to train them to be handled.