Nova Scotia has a provincial policy that daycares and registered dayhomes must follow-I just use that. It lists exclusion criteria (like fever, diarrhea, rash, etc) and how long they need to be out for. I allow kids to come with clear runny noses, and just follow them around all day with Kleenex and disinfecting wipes. It's a pain (esp in young ones that mouth toys), but they will get sick, and I just try to stop the spread (because then it's an endless cycle!).