TradeWithMe - why have you posted a useless link that has nothing to do with kittens?
It could be allergies since cats can be allergic to lots of the same things humans are like pollen, house dust, etc., but I wouldn't worry unless they seem 'out of sorts' in any way, like sleeping & lying around more than usual or eating less, or they get some kind of discharge from their eyes or nose since they are fully vaccinated. It is possible for kittens to catch a virus that can slow them down & put them off their food for a few days but unless you've taken them to a cat show or newly exposed them to the local cat population it is unlikely. Just watch them for more symptoms over the next few days - I suspect that it will be nothing but watching them is fun & costs nothing! Good luck.