the impression I got from the article is that it's a somewhat unsolved problem. the article mentions an "old friends" hypothesis that suggests that it's not exposure to dangerous pathogens that's important in childhood, but exposure to benevolent ones. but yeah, you're right, it's semantics really. kids have a different kind of strength. I would actually suggest it's quite analogous to brain development. kids are more adaptive and I'd argue creative, but adults are more experienced.