I don not own BBC Sherlock, they are the creative works of Steven Moffat, Mark Gatiss and of course the wonderful Sir Arthur Conan Doyle.

Well, I do hope you like this one. It hasn't been beta read, as I am still looking for one for this one. If you want to beta this, or my other Sherlock Fic, please PM me.

There is no slash in this fic at all, its all family and friendship. I do hope you all enjoy it!

The Science of Youth

Prologue

Sherlock and John ran into the warehouse. They went thought several rooms and corridors but were soon stood in the middle of a large room that they had chased a scientist by the name of Dominic Underwood. The forty-eight year old man that had been going around experimenting on the unsuspecting people of London. So far none of the so-called effects from the gasses had been good, and five people had died as a result of this mad scientists attempts at eternal youth. The two looked around the room; Underwood was nowhere to be found. Standing innocently in the middle of the room was a small device, no larger than the skull that normally sat on the fireplace back at Baker Street. The two men looked at one another, the device was exactly the same as the ones that had been found at the crime scenes.

"Sherlock, I think we need to wait for Lestrade to arrive, he said he would be here in a few minutes. That if we see anything strange or like what was at the scenes we should leave it all alone and take a step back," John told Sherlock, hoping that the other would listen for once.

Sherlock glanced over to John with an almost pleading look in his eyes as he spoke with a slight whine, "John, we lose valuable clues by waiting, and we don't want this killer to get away just because we waited, do you?" it was the way that Sherlock said those words that caused John to cave once again to the younger mans wishes. The Ex Army Doctor really needed to better learn how to resist his flatmate.

"Fine, but if you notice anything that looks like it might set something off, then move your arse away from it and don't touch anything else." He spoke sternly, getting a smile from the other as the two of them walked a little closer to the device in the middle of the room.

Sherlock looked at it carefully as he walked around it slowly. Looking at it from every angle that he could, taking in as much data as he could about it all. His pocket magnifying glass came out and he leaned in even more. The device gave a soft beep that John heard and he went on high alert, he knew that something was going to happen and he moved quickly, hoping to protect Sherlock at least. Something on the device flipped open, as John reached Sherlock and grabbed him. The consulting detective was too absorbed in examining the device to notice what was going on around him. John pulled him away and covered him with his body. Hoping to keep Sherlock away from the gas that was now being released.

The green gas enveloped the two of them completely, both of them held their breath for as long as they could, hoping that the gas would dissipate quickly. Seconds later John began to feel dizzy as he then collapsed on top of Sherlock. The younger man felt the increase of weight on top of him; he turned his head and frowned when he saw something weird. It didn't last long as his eyesight went blurry as he too blacked out.

XxXxX

Lestrade shook his head as he got out of his car, he already knew that Sherlock and John would have gone inside the warehouse, even though he had told them not to. He knew that John would always follow Sherlock, and Sherlock was the one that would ignore him, often dragging him into some sort of trouble. He walked into the warehouse warily, not sure what he would come across, he was a little worried as well since he wasn't getting any answer from the two of them, he had tried calling them a few times as he headed out to them and John always answered his phone. He walked further inside and came to one of the central rooms, in the middle of the room was a small device, and he knew by the sight of it that something bad had happened. It was open and he shuddered, it looked like all the others. It only became more apparent by the large bundle of clothing that was near it. He could see Sherlock's coat as well as John's, and the clothing that the two had been wearing. He slowly moved over to the clothing as it began to move slightly.

A child, looking to be around seven years old came out from underneath the pile first. A mop of curly brown hair and steel grey eyes told the detective the identity of the young one. He wondered a little if the same thing had happened to John. A part of him didn't even find it weird that they could both be kids, instead of their normal adult selves, being around Sherlock for too long soon made the extraordinary feel ordinary.

"Come on John," came the higher pitch of the childs voice as he knelt. He would have been naked, if it wasn't for the overly large plum shirt that was now hanging off his thin frame.

"Coming," a returning voice came back from the bundle as it moved a little more and a jumper-clad toddler came out. The short messy blond hair and baby blue eyes told Lestrade that the younger child was John.

With a shake of his head, he quickly ran over to them, "Sherlock, John?" he questioned, his voice filling with worry, wondering if the two of them were actually all right. He knelt down beside them as the two of them looked up to him.

"Lessphard," John lisped, then frowned as he heard his own voice, "Bugger, phought I goths rid oph phaths," he huffed, annoyed.

Lestrade frowned at him and automatically said, "John, language."

Sherlock looked at the Detective Inspector as he said, not concerned that his voice was now higher than normal, "Lestrade, just because we look like kids, it doesn't mean that our minds are that of children, so please don't insult our intelligence." John grinned a little at that remark, though it hadn't really sank in for the de-aged doctor, that the two of them were actually children now.

Lestrade couldn't help but say, "Sorry, but you two look like little kids at the moment, and John, sorry buddy but you actually look like a toddler." A slight smile on his face as he looked to the younger of the two.

John growled a little, but all Lestrade wanted to do when he heard it, was laugh at how cute it sounded. "I'm phive, I've alwaysss been phmall phor my age." He told him, once again annoyed at his genes that left him smaller than those around him. He was still a little smaller than most, even when he was an adult.

Lestrade shook his head in disbelief, "I thought you might be around three, and how old are you Sherlock?" he asked as he turned to looked at the young genius.

The older kid looked from the almost pouting John to the Detective Inspector, "I'm seven," he answered simply.

Lestrade nodded, he had thought that for Sherlock, but wanted to be sure. He turned back to John and smiled as bright blue eyes were looking up at him, "Right, I have a feeling that we should get the two of you somewhere safe. I don't think either of you want the general public and some of my Yarder's to see you like this."

John nodded his head as he spoke quietly, "Phat would be bessths." It could be a problem if the wrong people got hold of the information that they were vulnerable.

Sherlock nodded as he grimaced, an unpleasant thought coming to his mind, "I really, and I truly mean this, really hate the thought, but I believe that we may have to rely on Mycroft for help on this. He has resources we don't." He sighed in annoyance as he muttered under his breath, "Let's hope he doesn't enjoy it too much."

John and Lestrade looked to him in confusion, as John piped up, his voice high and almost squeaky as he asked, "Why do you phay phaths?"

Sherlock looked to him and answered quietly, "When I was little, Mycroft had a habit of always trying to pick me up and cuddle me. He is a nurturer, and since he is twelve years older than me, he did it as often as he could, not that I minded when I was very young. He just didn't stop until I told him to leave me alone and he went off to university, when I was around seven. Let's hope he doesn't try it again or this time his umbrella will end up in a better place." He threatened with a growl, which Lestrade thought was just as cute as John's.

Lestrade was just about able to keep a straight face as he said, "I'll give your brother a call and tell him what's going on."

Sherlock looked to him and asked him, "And how did you get his number?"

Lestrade chuckled at that, "Your brother gave it to me ages ago, and when ever it changes he always sends me the new one. Just in case something happens while you are with me and he needs to be informed."

"I don't like that." Sherlock pouted, not liking the fact that Lestrade and Mycroft kept in touch about him and what he was up to.

"Anyway," Lestrade said, making sure that Sherlock didn't go on a rant about his brother, "Why don't you boys go and get the coats, I can see that you're both cold. So wrap up warm for a bit." He said as he stood up and went to one side, glad that he hadn't brought Donovan with him, who knew what she would have done seeing the two of them like that, she didn't exactly come across as kind where Sherlock was concerned.

Sherlock watched as Lestrade walked away and then turned to John. He could see that John was shivering a little, it was the middle of December, and Christmas was just over a week away. He went over to the bundle of their now, too big clothing, and pulled his heavy coat from the pile.

"Come here John," he coaxed gently, as the smaller child moved over to him and Sherlock wrapped the coat around the two of them and then sat them down on the pile of cloths. He frowned when he could still feel John shivering and wondered if the younger boy was actually going into shock after he had thought about their unusual situation and let it actually since in a little.

"Phanksss," he lisped as he tried to get warm, but couldn't, cuddling a little bit closer to Sherlock.

Sherlock wrapped his arms around him even tighter and pulled him as close as he could, until the younger boy was sat on his lap. He pulled the thick coat closer around him as he said softly, with a little worry in his high voice, "It's all right John," he murmured as he hoped it would help John feel better, not sure what he should do in this type of situation.

Lestrade walked back over and frowned as he saw the worried look on Sherlock's face, "Everything all right boys?" he asked as he knelt down in front of them.

Sherlock looked up and turned worried eyes to him and said softly, "I think John might be in shock. He can't seem to get warm."

Lestrade turned to look down at the small blond, Sherlock opened the coat and stepped out of it, grabbing John's smaller coat to keep himself warm, it wasn't as thick as his own, but it would do. Lestrade smiled to Sherlock as he said, "Let's get the two of you out of here and to somewhere warmer, your brother is bringing a car. He'll be in it and driving. He's also bringing some of his people with him to take care of things.

"I don't know if I would trust my brother to drive," Sherlock murmured to himself.

Sherlock then watched as Lestrade picked John up and settled him in his arms, cradling him like a baby, "You all right John?" he asked softly as he made sure to wrap the tiny doctor up in Sherlock's thick coat.

John couldn't help it as he snuggled closer to Lestrade as he mumbled a little before he answered, "I'm phine." His voice was quiet and sounded tired as he spoke.

Lestrade rolled his eyes as John yawned a little, his bright blue eyes closing a little more each time he blinked. Greg and Sherlock walked out of the building and stepped towards the first black car that had pulled up. Anthea holding the door open and taking the Lestrade's car keys from him, as two more cars pulled up behind it, and more people getting out. Anthea nodded to them and then went into the building, the others following her. The Detective Inspector settled the now sleeping John into the car seat that was installed and made sure that Sherlock was secured in his as well, then got in the front with Mycroft, who soon had them speeding away from the warehouse and towards his home.

I have gone through this three times, and I have no doubt that there are still mistakes that remain. I apologise for it, and for those that tell me to get a beta, I am trying. I've just not found one, so if you wish to beta it for me, then please PM me!