4 day old chick seems "off"

[DoulaLiz]

I have 3, 4 day old chicks that were hatched out by the mama hen and have been outside with mama hen since. They have fresh water and started feed, they have been eating, drinking and all out walking around (in their enclosure) together over the last 3 days. All seemed fine, we've spent a lot of time watching them, Today one seems withdrawn from the rest, mama and 2 babies are out eating, pecking, drinking, learning and chirping. Not pasty butt. This one is standing alone and appears to be breathing heavy. I don't want to intervene for fear of making mama mad at him and her killing him, but I don't want to let him die if I can help him. Are there some things I can try? Is Coccidiosis a possibility? TYIA!