Disclaimer: definitely don't own Sherlock, rights go to its respective owners.
It was a beautiful day. Of course, this was not commonly found in London, so as a result many people flocked to the parks in the busy capital.
A young boy of about 8 years sat in the sandpit. He was bored to death, obviously. Parks were not his thing, but Mummy insisted, and Mycroft being his goody-to-shoes self didn't do anything to alleviate Sherlock's misery. Sherlock dumped himself into the sandpit, not caring about dirtying his clothes (unlike Mycroft who wouldn't do "such a thing, it would taint my clothes!" whilst waving that stupid umbrella around) and crossed his arms. Oh no, he was most definitely NOT sulking.
"Erm, hello!" A voice called, quite unsure of itself. Its owner soon appeared in Sherlock's view. The boy was probably 2 years younger than him and had blonde hair. He was also wearing a terrible hand-made jumper, complete with crazy stripes and zigzags. Sherlock cringed inwardly.
"Hello," Sherlock replied, albeit a bit gruffly. He could not see what this boy wanted, and frankly he was disturbing his thinking time, he needed to get back at Mycroft. "What do you want?"
"I... thought we could maybe play together?" the boy queried cheerfully. Play? What sort of idiot did that child think he was? Sherlock didn't play, he was brilliant and deduced and conducted dangerous experiments, (although he never got far since he couldn't properly reach the lab table). It's not as if he was sat in a stupid sandpit playing with the sand... oh wait. He was. Damn it. There was no way out of this then.
"Fine, but you mustn't be annoying," Sherlock didn't hold out much hope, but it was worth a shot.
"OK! I'm John! What's your name?" John really was quite enthusiastic. He had seen this mysterious boy and he looked quite interesting.
"Sherlock," was the reply. Even more interesting then. The two sat down together and before long John was showing Sherlock how to make sandcastles with his bucket and spade. Sherlock was impressed but of course, he didn't show it. It also didn't help that Sherlock was terrible at it, and John giggled at him endlessly. Honestly, what sort of boy giggled? But it seemed to be infectious and even he let out a chuckle now and again.
They were getting along swimmingly when Mycroft, had to ruin things (of course; that was to be expected, he was Mycroft after all). Mycroft came up to the pair and smiled down at them, and as per usual, the smile looked more of a grimace.
"Well what have we here, young Sherlock making friends with John?" his tone was mocking, and John didn't like that one bit. Forgetting the fact that this kid somehow knew his name, John stood up.
"Don't you tease us! He's very nice and at least he's not ugly like you!" John retorted using 6-year-old insults. Mycroft raised an eyebrow.
"I see. Well this is certainly interesting, I believe the say goes 'John and Sherlock sitting in a tree', need I go on?" The smirk that followed was pure evil masked by politeness. Mycroft turned and left, swinging his precious umbrella along the way.
Sherlock was not pleased. He remembered his original plan for revenge, and thought it was time to let John into it. He beckoned John over, and told him about Mycroft's secret cake stash, and his precious umbrella. Together they devised the best way for Sherlock to sneak in and destroy the stash using the umbrella. It was genius, and Mycroft wouldn't know what had hit him.
The two enjoyed the rest of the afternoon together without interruptions from Mycroft. All good things came to an end, and when the sun began setting it was time for them to part. As their respective mothers took them home John waved to Sherlock and Sherlock smiled. Something in the smile told John that they would definitely meet again one day.
(Mycroft's cake stash was utterly destroyed, and his favourite umbrella just happened to have the glazed icing from his doughnut on it.)