Disclaimer: Not mine. Not making any money.
Warning: Scatological humor
George and Fred Weasley were a month shy of five years old when their little brother Ron turned three. Ron was annoying—he broke their toys, and their mother paid more attention to him than to them. It was time to get him back.
They waited until their mother was behind the house feeding the chickens to confront their brother.
Ron was sitting in the living room, seated on the floor, and bent over with his rear in the air. He didn't hear George and Fred approach, as he was intently playing with some toy cars his father had given him, making "vroom!" noises as he passed them over the carpet.
"Hello there, Ron. What are you doing?" George asked.
"Playing cars. Daddy gave them to me for my birfday. They're mine."
"We know," Fred replied. "But we got you a present, too!"
"Yeah, we got you a present too!" George reiterated.
"A very special present!"
"Just for you!"
"And we made it ourselves!" they exclaimed in unison.
Ron looked at them warily. His brothers were not normally nice to him. Well, Billy was, but he was nice to everyone. George and Fred were not nice.
"What is it?"
"It's your very own cupcake!" Fred replied.
"And you don't have to share it with anyone, Ronny!" George added.
Ron was still skeptical. But he loved cake. And he always got such a small piece. At least he didn't have to share his cake with Ginny. She was still a baby.
George and Fred pulled the cake out from behind them and presented it to them. It was a chocolate cake, with loads of chocolate frosting and sprinkles.
Ron sighed. Chocolate cake was his favorite! Mommy always made vanilla cake, which was Percy's favorite. He didn't like Percy.
Ron reached his finger out and dipped it in the frosting. He put his finger in his mouth and tasted it—it was so good! He grabbed the large cupcake with both hands from the plate they held and shoved a large portion of it into his mouth, smearing frosting all over his hands and face in the process.
Fred began to snigger, and George clapped his hands over his mouth. Ron's face turned white as he actually began to taste what was in his mouth.
"Poo-poo?? You made me eat poo-poo??" he said, spitting and clawing at his mouth.
"Happy birthday, brother!" The twins fell to the floor, bodies shaking from the giggles.
But then, Ron surprised them both. Usually, Ron was too scared of his twin brothers to stand up to them, but this time, Ron knew exactly how to get them back.
Screwing up his little face, he began to wail, tears rolling down his face.
"Muuuuuummmmmmmyyyyyyyy! Ron screamed.
George and Fred looked at each other, panicked.
Ron took a deep breath, looking at his brothers with pure malice, before screaming once again.
Fred looked at George, panicked. "Time to go, brother!"
Before their mother could find them, they bolted out the front door, running towards the Lovegoods'. Maybe Mrs. Lovegood would tell them stories and feed them some Plimpy stew! In any case, they knew Mr. Lovegood would never turn them in to their mother.
AN: Based on a prompt by luvsev: "The Weasley twins first prank. Who did they pull the prank on and what was the reaction?"