My daughter is nearly 3. She had a runny nose yesterday and we stayed inside and warm as much as possible. She had a bad night coughing and I didn't send her to pre-school this morning.
My feeling is that at this age they are not missing much and get better quickly if they are kept at home until they are better. They don't infect anyone else with their germs and their coughs/colds don't get bad.
What do other people do and why?