Teething generally produces clear snot .... Coloured snot is generally viral which is why the rest have picked it up. Some kids always seem to have a runny nose..... Some kids would never be at daycare if they were excluded for every runny nose .... So generally if it is coupled with coughing/hacking, sneezing and the inability to cope in daycare then I would ask the parent to give them a day at home on the couch to recoup... Especially if its a Friday