When to keep kids home sick from school?

This probably belongs on /NoStupidQuestions but, my son just started preschool for the first time a couple of weeks ago. He's sneezed like three times last night and 3 times this morning. His nose is very slightly runny. Otherwise, he doesn't seem sick at all. No fever or cough, etc. It could be allergies as we all suffer from them and I've been slightly sneezy the last few days with no other symptoms. What is the etiquette: do I assume he's sick/getting sick and keep him home today from his 3 hour preschool class? Or should he be more obviously sick for that? I'm thinking of taking him but telling his teacher he's sneezed a few times and she can call me to get him if he seems sick...? Sorry, new to all this :) via /r/Parenting https://ift.tt/2QobADA