If there are coccidia in their environment, they will be infected. The goal then is to have a slow exposure so the chicks aren't overwhelmed by too many parasites at once at too young an age. Sometimes then it's necessary to treat them for infection to prevent serious illness/death. Never happened here, yet.
I don't feed medicated chick starter, but wouldn't hesitate to use it if there was EVER a problem with coccidia here. Mary