I would not throw medicines at them too quickly. Look at your brooder ventilation, prevent dust and keep things very dry and clean in the bedding, making sure they don't spill water in the shavings creating mold. Were the chicks from a hatchery or feed store? Or did you raise them? I would look at this being something irritating, unless more symptoms occur. Some respiratory diseases can be carried to chicks by exposure to older chickens, and mycoplasma (MG) can be passed through hatching eggs or from a broody hen. Usually, you won't see respiratory symptoms for a couple of weeks in those chicks.
