They have bags of chick grit at most Tractor Supply stores, or you can use sand from your area if you have any where you are. It should be very small granules, not like the size for grown birds. Newly hatched chicks will not be off the nest with their mommas for a couple of days. They will then eat whatever their momma says is good for them, included grit from the ground.
If you want to give them a treat, try a scrambled egg instead of a dried meal worm....easier for them to digest.