It was in their motel room when Sam had the thought. He interrupted a rather hot make-out session with Dean to say, "I want to go rollerskating."
Dean blinked, then groaned. "Dude, please tell me you're possessed or something. ‘Cause otherwise, no reason you should be sayin' that with my tongue down your throat."
Laughing, Sam hit Dean's shoulder playfully. "I'm serious, Dean! I really want to rollerskate."
"Enough with the whining, get back to the kissing." Dean made for Sam's lips again.
Sam huffed, then pushed Dean off of him and got up. "And I want a swing set. With a slide. And a tire swing."
Sam's eyebrows shot up just as he snapped his fingers together excitedly. "Oh! And a pony! And a cowboy hat."
Dean blinked again.
"To go with the pony," Sam explained patiently.
Dean let out an exasperated laugh. "You mind explaining to me why we're both hard and you're going on about ponies? If you wanna ride anything, it should be me."
Sam rolled his eyes. "I really want those things, Dean."
Shrugging, Dean replied brusquely, "So buy them."
"With what money?"
"Steal them, then."
"Steal a pony?"
"Whatever works, dude."
Dean sighed. "I'm sorry, Sammy, I'm just not following you here. What do you want?"
Sam looked pointedly at Dean. "A childhood, Dean."
Dean raised one eyebrow. "Come again?"
"I want a childhood." Sam sat down next to Dean on the motel bed. "A normal, average, elementary school, trick-or-treating in October, pool parties in July childhood."
Dean ran a hand through his hair. "Sammy, you know, me and dad, we did the best we could. I gave up a lot so that you could be a kid, man. But it's time to grow up now."
Sam tilted his head down. "I know all that. I know you did the best you could. I know you gave up a lot, I'm not saying you didn't. But Dean… What were you thinking? I want a childhood with you, with my older brother. Not just by myself. I just wish you wouldn't have given up on a childhood yourself, is all."
Clearing his throat, Dean awkwardly replied, "Yeah, but Sammy… That's how we survived. You're lucky it was me that had to hunt with dad. You were too much of a wuss back then anyway." He punched Sam playfully in the shoulder.
Smiling, Sam lifted up his head. "Yeah, that's probably true. Still, don't you wonder about how it could have been?"
Dean nodded shortly. "Yeah, sure, sometimes. I mean, who doesn't wonder about how things could be different if this happened or if that happened? Everybody wants to know that. That's just life, man."
Sam kissed Dean once, gently, on the mouth. "Do you think this would be different, if we were regular kids back then?"
Dean shrugged. "I sure hope not." He leaned in to kiss Sam again. "Now can we finish already?"
Smirking, Sam nodded and climbed back on top of Dean.