Exposure to germs and allergens is good for kids and helps build their immune system.

https://www.npr.org/sections/health-shots/2017/07/16/5370750...

>After the birth of his second child, Gilbert, a scientist who studies microbial ecosystems at the University of Chicago, decided to find out what's actually known about the risks involved when modern-day children come in contact with germs. "It turned out that most of the exposures were actually beneficial," Gilbert says. "So that dirty pacifier that fell on the floor — if you just stick it in your mouth and lick it, and then pop it back in little Tommy's mouth, it's actually going to stimulate their immune system. Their immune system's going to become stronger because of it."

https://www.nature.com/articles/nature.2012.10294

Hope that helps!

I don't think this applies to the first three months when contact should be more limited due to an undeveloped immune system.