Actually children who are socialized with other children even in unorganized events such as playing together in the park are all around more healthy than children raised in sterile households with minimal contact with other children.
If children are exposed to more germs in the first year of life they develop more immunities that last through their lives.
Similarly the ubiquity of anti-bacterial soaps (especially in the States) can be detrimental. These soaps kill off many bacteria but the bacteria mutate such that they are immune to common antibiotics. A few decades ago there were antibiotics to fight almost every bacterial infection, recently multidrug resistant bacteria – staph, mycobacteria that cause TB and others- are trumping the drugs we have to fight them.
So getting a little cold, or being exposed to a few germs at an early age builds immunities that can fight of those and similar infections better than children who were denied contact with those other germy little rug crawlers.