Does being sick frequently as a toddler really pay off in the long term?

A few parents that I know keep bringing their sick children (colds, flues, etc.) to see my son. They're all about the same age, around 18 - 24months. I know toddlers get sick more often because they're always putting things in their mouths, and I expect that to a certain degree, but when they knowingly bring their sick toddlers over and then my toddler gets sick it's kinda frustrating. And doubly frustrating when they respond with "oh well, it builds their immunity, they'll be better for it in the future". I don't know if I agree with that, so I'm asking here for evidence either for or against that.I guess I have a few questions:1) Does getting sick early and frequently really pay off long term? I've read news articles saying that it does, but does it really pay off? If a toddler has to get sick dozens of times a year just so that they can avoid one or two colds in adulthood that's not really beneficial. Is there data somewhere that shows me how effective this really is?2) Why do we bother telling adults to stay home sick so that the elderly and young won't get sick, but then turn around and act like everything is totally fine when toddlers spread it?3) Do you bring your baby, toddler, or child to visit other babies, toddlers, children when they're sick?4) Would you be ok with other parents knowingly bringing their sick baby, toddler, child to visit yours?Looking forward to hearing how other parents feel about and deal with this. Thanks!EDIT: I'm very, very interested to hear if anyone has a book recommendation that describes how colds, flues and other common sicknesses (especially ones we typically catch as children), and how they're transmitted, how our bodies fight them, how the immune system works, etc. If anyone knows of a book like that please post it! I love reading non-fiction so even if you found it to be very dry or boring I might like it. via /r/Parenting https://ift.tt/2qrZiyY