Here's my take on it:
Runny poops are normal, as long as they are not occurring 100% of the time. Cecal poops are often runny, and very stinky. Often look like chocolate pudding. Give those chicks some soil or sod from your yard. That will build their gut flora and give them gradual exposure to any cocci present. You want to do that BEFORE they move out into the yard and get hit with a big cocci load on their first rainy day.
Never give an antibiotic as a preventative.
ACV: If you use it, be sure to offer plain water also. Perhaps one waterer with, and one without.
I strongly suggest that you look into using fermented feed for the many nutritional advantages it provides.
I have never used medicated feed, and I've never had issue with coccidiosis in my birds. Some would suggest that my soil has a lower load of cocci. Possible? Who knows. I've had chickens on this property for 4 - 5 years now, and previous to that for 7 - 8 years as well. One thing that can help your yard to stay healthy is not allowing your run to turn into a barren moon scape: mud pit in the rain, dust bowl when it's not rainy. That can be accomplished with deep litter which will do a lot to keep your soil healthy. Again... lower load of pathogens highly likely with deep litter!