It’s like clockwork. With the arrival of cold weather come winter colds and sniffles, posing the inevitable quandary for parents: How sick is too sick to send your child to school? Sometimes, it’s obvious. If your child is feverish and shaking or vomiting, he or she is probably in no condition to be learning. But what about a nagging cough or sore throat? Canyons District encourages school employees and students to stay home when: They are not well enough or seem too…