My nephews are in preschool and our main concern always at this stage in their lives are their health and learning development. It used to stressed us a lot because preschool age is the stage wherein kids immune system is still developing therefore making them more susceptible to sickness like cold, coughs, asthma, allergies, and other infections. Almost every week, one of them is either down with flu or nursing an allergy. If that scenario is not stressful, I don't know what is.
What more stressful about it is the fact that the kids are missing the opportunity to enjoy and learn new things at school because of their ailments are keeping them at their beds. The sickness was putting a halt into their learning development and it was really concerning.