A plug of grass with the dirt and roots attached will make it easier for the chicks to nip pieces of grass and expose them to soil. Better than clippings. Give them some chick grit with, mine get this at 2 days old.
That dirt has all the junk in it from your yard and helps them build immunity. I also give my chicks a pan of dirt from the floor of my coop for dust baths at this age, good exposure for building their natural immunity as well.
They can have small quantities of anything you want to introduce. Momma Hens raising Chicks definitely start them early on everything. The Hen isn't out there telling them to spit certain things out.
Just provide Chick Grit also..