Oh, yeah, the mini!Sam and mini!Dean fics are probably the biggest exception to that no-comedy rule. I will continue to maintain that five-year-old Sam must have been the most adorable thing on the planet, if for no other reason than I keep picturing big brown eyes and lots of thick dark hair and tiny little sneakers and continually asking nine-year-old Dean fifty-five million questions in a row. :)

Is Beaver/Mac canon now?

Uh-huh, and it's beyond adorable. It comes very, VERY close to trumping five-year-old Sam in the cute department. ;)