What dangers could emerge from not being exposed to a variety of bacteria and viruses in childhood? none

When : When you say being "exposed, " i'm going to assume you mean being infected with. So... Being infected with a bacteria will not make you any more or less susceptible or immune to any future exposure to that bacteria. Our bodies do not build immunity to a bacteria, only viruses. Thus, you can get a strep throat again and again and again, and no amount of getting a strep throat will ever make you immune to getting another strep throat. Viruses are different, and once exposed or infected with a virus, we can develop immunity to that particular virus for a period of time. Depending on the virus, immunity can last anywhere from days to years. Viruses mutate (change), and a slightly different virus of the same sort can infect you even though you've had a strain of that virus before. It's iffy. But even if you never had the usual "childhood diseases" (viruses), i assume you've been vaccinated against them, in which case, you're fairly well protected from future infection of whatever viruses you've been immunized against.

Immunity: One can develop a certain amount of immunity to some types of viral infections. That is the biggest issue. Vaccinations can also help to prevent some types of infection.