Best thing to do is put dirt from your property into their brooder, like in a shallow pan, and make them a little dustbath so they are exposed early on, from the first week of life. That's what would happen if they were roaming with a broody mama hen-babies raised by broodies rarely, if ever, get cocci, for some reason.
Then you watch for symptoms of coccidiosis and seek out a source of Corid 9.6% solution, just in case. Fluffed up, lethargic chicks and bloody poop are signs of coccidiosis. Even chicks raised on medicated feed in a brooder, with no exposure to dirt, when suddenly plopped outside at 4-6 weeks old, can be overwhelmed by the oocysts in the soil that cause cocci.
What many don't know is that chicks can hatch with oocysts in their gut already, then when they hit soil, if they haven't been exposed to it in the brooder already, they can get coccidiosis within a week or two.
And, by the way, cleanliness in the brooder is NO guarantee against cocci, in spite of what others may say! It should be kept dry and the water free of poop, certainly, but it's not a guarantee they won't get cocci even if you are the Martha Stewart of Brooder Cleaners.