unless an antibiotic is called for, you could keep them off and then when they go back 3 other kids would have a snotty runny nose so you're fighting a losing battle. unless the nursery say no . i told mine last week dd had diarheoa and to ring me if anything happended but nothing did and they were fine with htat.
if you have 30 children in a building at this time of year how many will either be finishing, starting or in the middle of a cold?