Brooder pneumonia?

I recently stumbled on little chicks at one of the local farm supply stores (I know, probably not the most intelligent decision to get them from there, but what's done is done.). Anyway, the coop was almost ready and we went ahead and bought 8 pullets. I lost one to what I think may have been brooder pneumonia (I guess it's still called that? It's been a while). Anyway, she tanked then rebounded then crashed and burned pretty quickly so there was really no opportunity to separate her from the rest. And today when I cleaned the brooder I thought I heard one sneeze / cough / peep strangely. Is there anything I should be doing to protect or treat the remaining chicks? My best guess at age is 6 - 7 weeks. Most of them are pretty well feathered out except for their heads which are still downy. I have no idea what breeds they are if that's even relevant. THese girls are my kids' future 4H projects, anyone have any advice?