Are adults more likely or less likely to develop shingles if, every few years, they come into contact with children who have chicken pox?

Depends...: ...On how high your chicken pox antibody titre is. As we get older our antibody levels diminish, and it is thought that when the level drops below some unknown threshold, the next exposure to chicken pox will trigger shingles. (there may be other triggers as well.) the risk increases as you get older, which is why the shingles vaccine (zostavax) is recommended after age 60.