When I was a kid, the word “behavior” still had a mostly neutral meaning. You might hear the word when Marlin Perkins on Wild Kingdom described the doings of a parched hippo during the dry season, for example.
But even then another, much more accusatory, meaning of the word behavior was establishing itself. This behavior referred to things kids did that grown-ups didn't like. “You'd better change your behavior, junior!” an evil vice-principal might yell, when we thought we were just having fun.