Hi A.,
This is a common misconception. Getting sick does not raise the immune system. Especially repeatedly. Health raises it. Not getting sick is not necessarily good health. My kids take care of sick kids in the nurseries at church and never get sick, even kissing on them, not because they are "super-kids" but because I keep them away from things that would brake down their immune systems. Don't feel bad, it took me a looooong time to figure this out and there are still a lot of people that will tell you differently.
We don't eat fast foods or processed ones except when in a bind. I give my girls a good absorbable multivitamin every day. No diet will give them all the nutrition they need. Even the FDA says that the soil is so depleted and the pollution is so bad that we don't have a chance with just food for our nutrition. I have detoxified my house, down to the shampoo they wash their hair with, from all synthetic chemicals so my girls have a fighting chance with their health. Even if you detox at home, remember daycares have multiple, powerful, synthetic chemicals that break down the immune system.
I understand your son is too young to chew a vitamin, :) but starting good habits now will help. If you understand the concept, it is easy to do and it doesn't have to be expensive or time consuming. Whether you put your kids in daycare now or in school later, is your decision. I'll be glad to give you more details on the path I took if you're interested, just let me know.
Regards,
M.