"I'm fine," he said in response to her question, and looked up as she instructed. It was pretty obvious it was a dream by then, and he didn't look openly upset about anything at least. "You're not supposed to be here, are you?"

Actually, his voice sounds older. Because he is older. It's a seamless transition, much the way it would be in a dream. Much like every other transition would be, except the magic is not quite there when you realize it's a dream. And Mako looks a little embarrassed, too, at what she's seen. It wasn't like he was the most gracious of kids growing up, and how often he got in trouble wasn't anything to be proud of showing.

"... Yeah, pretty sure you aren't supposed to be." His dreams of Korra never intersect with his dreams of his parents.