Marcellus: yes, their immune systems are not as developed and strong as adults but from what I have read it does seem that there is a connection to strong immunity and mild and regular "attack". Hence the reporting of the theory that many Western homes are too clean... that our love of sterile conditions are doing our immune systems no favours. Check out the thread about the benefits of letting your kids play in the dirt for example. Antibodies are created in our bodies (young and old) as a response to invading microbes. No microbes no response. White blood cells (these are the ones that basically "swallow and destroy" germs) need to be built up by a mild and regular attack. If a strong and sudden attack by a nasty bug arrives on the scene then an immune system that is used to being sheilded by sterile conditions is caught unprepared then the child will probably get much sicker than if the system was used to fighting lesser attacks. Does this make sense?