I've seen some of my birds drool a bit before. I've also seen them regurgitate a little bit of water as well. Are they eating and drinking normally? Any discharge from the eyes or nostrils or wheezing? If anything, it will more than likely be respiratory. If you don't see any of these symptoms and the birds are behaving normally, I'd say you're fine. If the weather is hot, this is pretty typical behavior. As far as stunted growth, just as in other animals, there can be "runts" in hatches pf chicks. Smaller, weaker birds with various defects can hatch out of a clutch. I had a GLW hen that was not a bantam, but not nearly as big as her normal counterparts. She also had a severely twisted beak that rendered her almost completely unable to eat without assistance. We cull birds like this here.
