Dean was worried. Sammy was hot; way hotter than he should be. Dean wanted to take Sammy to the doctor, like Mommy used to do for him when he got sick. But when he told Daddy, John pulled himself out of his chair and showed Dean how to crush a few little white pills and mix them into Sam's formula.
Dean bounced his brother on his knee to get him to stop crying. Then he fed Sammy his bottle, patted his back to burp him just like Mommy showed him. Then he sang him "Hey, Jude" and rocked him gently. When Sammy finally fell asleep, Dean laid him down carefully in the crib. He turned to climb into his own bed…but he never made it there. John found him a few hours later, curled up next to Sam in the crib, his small hand wrapped around Sam's even tinier one.
When the sun peaked through the curtains the next morning, Dean woke up and felt Sammy's forehead. He smiled. The fever was gone. Dean put his head down and went back to sleep.
AN: The impact this one small line had on me was monumental. I started thinking about how Dean learned this trick. How he used it to take care of Sammy when John was still grieving over Mary. It practically wrote itself, and in five minutes I had myself a brand new headcanon. No one will ever convince me this did not happen.