The good news is that some kids could build an immunity to whatever sickness they are exposed to from the other kids. The trick would be to make sure you don't spend too much time around other sick children. So, that is the hard part. Some people can be less prepared if they never play in the dirt. Your body needs to learn how to adapt to germs, etc. That is part of how some good vaccines work in theory. Some vaccines are bad. But it is supposed to introduce some germs, bacteria, viruses, etc, into the body so that the immune system can build up some kind of tolerance to it, step by step. It is kind of like learning how to ride a bike with training wheels. Too much can be a problem. Too little can also be a problem.