Disclaimer I don't own Harry Potter.
It was the final day of term at Hogwarts during Harry's fourth year, before everyone got ready to leave Fred and George wanted to do a going away prank on Professor Snape. They made there way to the dungeons to Snape's classroom after "borrowing" the Marauder's map from Harry. "Quick before Professor Git comes back." Fred said as they re-labelled Snape's potion supplies "to bad we wouldn't see it." George said as he replaces Snape's potion supplies with different supplies. They took a couple minutes before finished messing up the potion supplies and made they way back to the outside to catch the Hogwarts express.
Snape returned to his office to make-up some potion he sells as a little side hobby to make a little extra money, he decided to get a little start before going to the end of the year staff meaning. He grabbed a few ingredients and bringing it to a boil then starting to added some of the ingredient to the potion and large explosion of smoke ingofed Snape.
A few minutes later everyone Hogwarts staff member were waiting for Snape to arrive in the Great Hall "This isn't like Severus to be late." Minerva said "I agree, Snape must have lost track time. Minerva would you please if you don't mind could you please go and get Severus." Dumbledore said Minerva gives him a nod and leaves the great Hall and hand over to Snape office.
"Where am I... Mummy and daddy are going to be so mad at me." a tiny little about six years old Version of Snape panicking to himself looking around at the unfamiliar environment as fear begins to over take him about the though of his parents and getting in to trouble he begins to shaking in fear as he hears the sounds of footsteps heading towards him and then a knock at the door "Severus, the meaning started a few minutes ago." said Minerva. How does she know my name? Snape said panicking as he tires to find a place to hide as Minerva knocked even louder "Severus, are you in there!" Minerva yells this time.
Snape curls up into a ball shaking and covering his hears, as Minerva walks inside and Snape frozen in fear she found him he knew he was trouble he tired to make a fun for it but Minerva caught him. "Please... I be a good please... Sorry please." Snape said in tears looking up at Minerva as she looks back in shock, confused and sadness at the small child "Severus.?!"