I've never attempted a Kid!Lock story before, so here it is. To my knowledge, no one knows Anderson's first name, so I just called him Peter...
In the story they are seven-year olds and Sherlock has got over his pirate phase, only to turn his ambitions to being an explorer!
Enjoy!

"We've got to get past this good-for-nothing-guard, John! He's blocking the way to our treasure!" Sherlock shouted out gleefully, poking his stick out in the direction of Gregory's tummy.

"That's not fair!" Greg wailed piteously, the lisp in his voice immediately apparent. "I don't like this game! You always make me the bad guy!" Sherlock jabbed the stick lightly at his chest, grinning. "Sherlock. Sherlock! Stop it!"

"Sherlock." The seven-year old whirled around, ready for another battle. He relaxed when he saw the familiar shock of blonde hair. "Maybe Greg could be an explorer too?"

"By thunder! Don't be ridiculous! That is an important position that only you and I hold…" He trailed off when he realised that John Watson was being serious. "Oh alright, then." He hated listening to John, even though he was the only person Sherlock ever paid attention to. "You can help us, Mr Lestrade. Our aim…" He straightened up importantly. "Is to find the stolen treasures of Baker Street!"

"Baker Street?" John asked. "Where's that?"

"How do I know?" Sherlock snapped impatiently before continuing. "First, we need to capture the enemy!" He pointed his play-sword out wildly, narrowly missing Greg and aiming the weapon at a boy and girl, quietly playing in the sandpit on the other side of the play area.

Silently, their leader motioned for his companions to follow him and John and Greg grabbed their own sticks, hot on his heels. As they approached the targets, they heard the conversation.

"Peter, would you like a homemade cake?"

"Oh, yes please, Sally! I'd like that vewy much!"

"I'll just pour some tea to go with it for you."

"Oh! Can Teddy have some too?"

Sherlock pulled a face, feeling sick. Never in all of his days of exploring had he come across such goody-goody children. Striding across, he stomped through the sand, destroying the carefully constructed castle and cakes. Sally looked at him in fury and stood up on her tiptoes, throwing sand at his face.

"You freak!" She shouted. "Why do you always ruin everything?"

Sherlock calmly wiped the sand away from his eyes. "Mr and Mrs Anderson – " Both children opened their mouths in protest, blushing furiously, mortified by the very thought. "I'm holding you prisoners on this here expedition. You'll be useful to bait the enemy." He grinned cruelly and snapped his fingers sharply. "Men! You know what to do!"

On cue, his companions held onto one prisoner apiece and began dragging them towards the great mountain that lay before them – in other words, the climbing frame.

Greg easily managed to take control of Sally, who writhed and shouted in vain, but John found himself struggling. Peter was not giving up the fight easily – and John was easily the shortest of them, which made it extra hard. The two of them squirmed on the grass, fighting to take the other on and determined to prove that they were the strongest. Luckily, John had an ally in Sherlock, who hauled Peter off his loyal comrade and helped pull him along.

At the climbing frame, they wrapped the ropes that John had 'borrowed' from his father around the kidnapped wretches and tied them to the wooden supports at the base. Sherlock cried out in triumph and agilely clambered up the frame, heaving himself to the very top of the timber roof and waving his stick proudly in the air. Then he stiffened and squinted into the distance.

"Egad!" His posh explorer accent was back. "The enemy's approaching – and they've got the stolen gold! Mr Watson! Mr Lestrade! To your positions!"

Obediently, John did a rather inelegant roly-poly to the base of the 'mountain', crouching in position, stick at the ready. Greg scratched his head, trying to work out what was going on, and then ran next to John.

"Hold!" Sherlock called. "Hold…! ATTACK!"

And suddenly the sticks were slicing violently through empty space as they tackled their imaginary enemies away, shrieking with laughter.

Above them, Sherlock was fighting off any invisible foes that dared clamber up his claimed land. Twice, he had to hold onto the wood tightly to stop from falling down.

Sally and Peter just sighed, rolling their eyes.

"They're so weird." The girl called loudly. The three boys playing ignored her, too engrossed in warfare to pay any attention.

Sherlock stood up unsteadily on the roof of the climbing frame, balancing precariously.

"I'm coming down!" He announced, focused on the three metre drop beneath him. John stopped fighting and turned to face him, looking up. His eyes went wide in fear at how large the gap was between his friend and the ground.

"No, Sherlock. You'll hurt yourself! Use the slide!"

"A good explorer always takes a dangerous path! I'll be fine, John!"

He bent his legs and braced himself.

"Sherlock…" John warned. Greg had also stopped now and was staring with trepidation. "Sher – Sherlock!"

Sherlock jumped.

John paled, frozen to the spot. Suddenly, he was filled with an overpowering sense that this was going to stay with him for the rest of his life. That Sherlock was going to die. That his last word would be John's name –

Sherlock landed on the grass, crumpled and still. Greg gasped. Sally and Peter peered at his body cautiously from their prison pole. John had already reached him and knelt next to him, a buzzing sound in his ears.

"Sherlock?" He whispered, shaking him by the shoulder. The black haired boy rolled onto his back, groaning, his eyes flickering open.

"John?" He muttered. His friend nodded, relief flooding through him, grabbing his hand. They ignored Peter's feeble attempts at a wolf-whistle. "My leg doesn't feel too good…"

"Can you bend it?" John asked softly. Greg cam over and Sherlock used his elbows to prop himself up, shrugging. His bottom lip was trembling ever so slightly.

"I'll get teacher." Greg said sensibly. "But I'd better release the two hags first." Sherlock let out a laugh that sounded more like a sob. Greg hurried away.

John kept a hold on his friend's hand, his eyes serious.

"You really shouldn't have done that, Sherlock. It was dangerous."

"I know." Sherlock replied weakly. "I should 'always listen to you'. But it didn't look too high –"

"Sherlock. You don't do that again. Do you promise?"

Sherlock bent his injured leg slowly, wincing.

"See? I can move it."

"Sherlock." John's tone was serious. "Do you promise?"

The wounded boy wiped at his watering eyes and nodded, his head bowed, squeezing John's hand hard.

"It hurts. I won't do it again. I give you my word."

"Good." John relaxed.

Their teacher, Miss Hudson, a slim woman in her early thirties, came quickly, Greg behind her.

"Sherlock –" She began, angry.

"I know." Her brightest and brashest student said meekly. "I shouldn't have jumped. I won't again."

"…Good." Miss Hudson echoed John, pleasantly surprised. "Well, we need to get you to the medical room."

Sherlock shook his head, his hand like a vice around John's. "It's okay. John here's going to be a doctor when he's older. He can take care of me."

His teacher couldn't refrain from smiling as the shortest boy in the class helped support the tallest boy up and onto a nearby bench. She overheard John's high professional voice as he tended to his patient.

"It's only bruised, but when you get home if it still hurts make sure your mummy puts some ice on it. Now, I'm just going to take your pulse… there. It's a bit faster than usual but that's coz you've been exercising, you know."

Miss Hudson risked a look at them. There was John, feeling Sherlock's wrist with intense concentration, trying to re-find the pulse. And there was Sherlock looking at him in admiration, hanging on his every word, the tears long gone.

He had learnt his lesson.

-.-

"Goodbye, John."

"Sher – SHERLOCK!"

Sherlock jumped. It was a long fall. And then he landed. John staggered over, as if in a dream. As if in a nightmare. This wasn't happening. Not now. Not again. Sherlock was going to die. And his last word would be John's name –

He arrived next to the fallen man, pushing past the crowd, his sight strangely blurred. He grabbed the hand. Like he had done all those years ago. Trying to find that pulse. Calling out his best friend's name.

No pulse. Nothing.

"I won't do it again. I give you my word."

He was dead.