sneezing 7 week olds

i have 8 black austrolorps 7 buff orphingtons and a buff orp roo that are 7 wks old so i was wanting to put them out this week i have the brooder in aspare bedroom and have only used puppy pads and drop cloths for bedding to keep dust down in the house i have a small air cleaner in the bedroom to help but now that they are nicely feathered and ready to go to the coop i have heard 2 of the buffs sneezing with slight wheezing in their chests . they have not been exposed to other animals dust is minimal i have no idea what i did wrong but dont want to lose any please help!! there are no fuids noticeable on nose or eyes poop is brown couple are a little runnier than others