The time stopped for Ralph at some point in his childhood. There are no actual signs of regression when you watch him because he doesn't regress back into his third grade self, he is his third grade self, laughing because dog is dead. He talks about kids from third grade in present tense i. e. "I know him well" as if 30 years between the events did not pass at all. You can't know the kid well Ralph because even if your development froze back then, chances are that his wasn't, and he developed into something other than the child he once was. That kid no longer exists outside your head.
Also a child carrying a small dog is not the specific sub-"type" of guys. It's a child with a pet, in his age of childhood innocence. Child that cried when you murdered his beloved pet, as would every normal child or adult. If by "that type" you mean normal disregard my ramblings. You were, and still are the sub-type of a child that laughs at dog's death. You had a "type" as a child that was distinct from normal children, you freely admit this, and you also admit that you've not grown at all since then. Truly a case to be studied.