Dean woke up in the middle of the night to Sammy's screams and rolling thunder.
He recognized the voice instantly and grabbed the knife from under his pillow as he searched the room for Sam, for the threat, but no one, nothing, was in sight.
"Sammy!" Dean yelled. "Where are you, what's wrong?!"
Sam started to say something, but crashing thunder from the storm outside drowned out his voice, and after a few moments, Dean could only hear the thump of rain on the windows and Sammy's soft cries.
Dean looked around for the closest place to Sam's bed that a six-year-old child could hide in-
Under the table.
A second after the thought, Dean was there. He dropped his knife, and the sound of his knees when they hit the floor as he knelt next to Sam was covered by more thunder and heavy rainfall. Sam was curled up in a ball, ears covered by his hands, face buried in his knees.
"Crap, Sammy! Again?" Dean said, boyish features frowning as he looked down on his little brother's tiny figure.
Every time there was a thunderstorm, Sam would freak out. He'll get over it, grow out of it someday, their father would say. Not to say he was a cold man, no sir. Sam was just a child, after all, and on those nippy nights, when John was home, he'd hold Sammy close and sing Hey Jude - just like Mary would when Sam was a baby, as she rocked back and forth, able to quiet his cries every time - till he could hear Sam hum along with him, his young lungs able to match the tune well; that's when he knew he was okay.
"I'm s-sorry, Dean, p-please…" Sam stuttered, his face twisted and wet from crying. He looked up, uncovered his ears, and stretched out towards Dean.
"Alright, come here," Dean said as he pulled Sammy into his lap.
The sound of thunder filled the small motel room again, and Sam jumped a little before more sobs shook his body. Dean squeezed his eyes shut for a second and sighed, he hated to see his little brother like this.
Then he cleared his throat, wrapped his arms around Sammy, and started to sing as he swayed to and fro.
"Hey Jude, don't make it bad…" Dean could hear Sam sniffling, rain tinkling-
"… just take a sad song, and make it better…"