I like shorts! They're comfy and easy to wear!
When you're going on an adventure, you want light, easy-to-wear clothes. And little boys tend to favor shorts because, like the page quote says, they're comfy and easy to wear. Especially when it's warm out and pants are just too confining. This is meant to portray younger male characters as innocent and lighthearted, as opposed to the more "serious" adult characters in long pants or heavy armor.
Boys in shorts is also Truth in Television
as in the past, the mark of a boy reaching manhood was his first pair of long pants.
- Rolf, Ewan, Asvel, Nils and Lugh of the Fire Emblem series
- The boys in Earthbound
- The Youngster class of the Pokemon franchise. Oddly, this is averted by all the male protagonists except Nate and the original Gold.