We use the powder, it doesn't take much and we haven't had any noticeable trouble with it. We only put it on the hen and let the chicks get it from crawling through her feathers. Use the spray to treat their nest area while they are out for a thorough cleaning. It will be dry by the time they are back.
If you can move the hen and chicks to a garage area for a few hours you can use the spray on them to avoid the respiratory concerns.
If you can move the hen and chicks to a garage area for a few hours you can use the spray on them to avoid the respiratory concerns.