London was a large city, and with every large city comes the homeless.
Sherlock had spent quite a few of his less productive, drug-addled days on the streets, so he felt sympathy for them. His homeless network was a way of helping them in a small way. A little money here and there did wonders. He couldn't give too much, of course, otherwise the money would go to the wrong kind of people, those who would waste it on alcohol and drugs like he had. No, he had to be careful who he gave it to.

The Irregulars were the ones he looked out for the most, the homeless children of London. They were a small bunch. He knew them all and, dare he say it, was slightly fond of them. They enjoyed helping him with cases too, when they could. Mostly small cases, even he wouldn't put a child in danger if he could help it.
Most of them got their meals about a mile or so from Baker Street, at a soup kitchen owned by a small family. The eldest daughter of said family was 28 year old Mira. She spent most of her time trying to keep the Irregulars in line.
The small group of kids ranged from ages four to fourteen, and because of the care Mira and Sherlock bestowed upon them from time to time, they had taken to calling them Mum and Dad. Sherlock didn't particularly like the title, but he wasn't fazed and it did help him get them out of trouble occasionally by pretending to be their father. This was one such occasion.

He and John were at a crime scene, just about to leave because he had some serious research to do on shoe laces for the case. Lestrade was walking with them, trying to follow Sherlock's reasoning for needing to take the murder victim's shoes when Donovan appeared from around the corner, two children running from her.
Sherlock recognised them instantly. The boy was fourteen, Joseph, and the girl was only four, Nina. Judging by how clean they were looking, they had been with Mira recently, and looked presentable, which was rare for the Irregulars. When the two saw Sherlock, their eyes lit up and they went straight into acting mode, something all street children were good at.

"Dad!" they cried, running straight up to him and wrapping their arms around his waist, looking afraid of Donovan. How this simple trick worked on everybody amazed Sherlock. In reality, the one thing street urchins were never afraid of was police.
Donovan's jaw dropped.

Actually, everybody in the vicinity who knew Sherlock had the same reaction, including John and Lestrade, who, despite knowing Sherlock a long time, had never seen the Irregulars. The kids always came by while they were away.
Mentally rolling his eyes, Sherlock played along, putting an arm around each of the kids.

"What have you two done now?" he asked dryly. "Joseph? Nina?"

"Nothing," Joseph answered, obviously lying. "She's chasing us."

"Were you picking pockets again?" Sherlock asked angrily. It was a habit he was trying to get the Irregulars to kick.

"We only took a watch," Nina murmured quietly, holding out the gold band.

"Nina!" Joseph growled, obviously frustrated she had given in so easily.

"I don't like lying to daddy," she said, looking up at Sherlock, crocodile tears in her eyes. Nina knew Sherlock wouldn't be fooled, but the display was more for the police officers than anything else.

"These are your kids?" Donovan gaped.
Sherlock nodded, and the two children grinned.

"Where are your siblings?" Sherlock asked. "You haven't got them out pick pocketing too, have you?"

"Nah, they are all back with Mummy," Joseph replied. "She's making us all take baths..."

"Mummy?" Lestrade choked out. "Siblings?"

"Sherlock wha-" John started, but he never got to finish. Nina jumped up into his arms, much to his surprise.

"Hiya, Uncle John!" She smiled and Sherlock chuckled. She then threw the watch to Joseph, who handed it guiltily back to Donovan.

"You can take it back to the man we took it from," he said. "We're sorry."

"I've got work to do," Sherlock announced to the two children who gathered back in front of him. "Go on, and no more stealing."

"Alright, Dad," they sighed, turning and running off, giggling to themselves.

"And stay on the paths I marked for you!" Sherlock called. He didn't like it when the Irregulars wandered into the slums of the city, they were dangerous.
Before the kids could disappear, however, Mira appeared around the corner looking furious. The anger disappeared when she saw the two a few meters from Sherlock and the police. She surmised what had happened when her eyes found their way to the watch in Donovan's hands.

"There you two are!" she growled. "Thank you for finding them, Sherlock dear."

Sherlock mentally rolled his eyes once more. Mira did like to mess with people a bit.

"I didn't, Donovan did." He pointed to the shell shocked woman who was staring at Mira. She quite obviously thought Mira was Sherlock's wife or something of the kind. Sherlock had to admit, messing with Scotland Yard was quite entertaining.

"Well, thank you," Mira smiled, "I've got to keep my eyes on so many of them, they tend to sneak away."

"We didn't sneak Mummy," Nina grumbled, "We went walking."

"That's mummy?" John muttered, confused. Sherlock nodded.

"Well, I think it's about time you two left Dad to do his work," Mira smiled, taking each child by the hand and leading them around the corner. "I'll see you later, Sherlock!"

"The freak has kids!" Donovan exclaimed finally, very worked up.

"Siblings?" Lestrade repeated, looking Sherlock in the eye. "How many of them are there exactly?"

"Fourteen," Sherlock shrugged. It was true. There were fourteen Irregulars and they all referred to him as 'Dad'.

"Fourteen?" Donovan spluttered.

"John, did you know about this?" Lestrade asked, turning to the doctor.

John made eye contact with Sherlock for the briefest moments. The detective could tell he didn't understand what was going on, but a small mischievous glint in his eyes told Sherlock he'd play along.

"Of course," John smiled. "Why do you think the flat is such a mess all the time?"

"You fit fourteen kids in that flat?" Donovan gaped.

"'Course not, they live with their mum. Sherlock's work is much too dangerous, so they visit," John continued giving Sherlock the 'You-better-explain-this-later-or-you-are-going-to-get-it' look.

"Come along, John," Sherlock called, walking away. "We have shoe laces to research!"

The minute they were out of ear shot, John had demanded an explanation. Sherlock told him the truth. He'd never lie to John if he could help it. Once he'd finished explaining, John roared with laughter, saying how glad he was that he'd played along and how they had to do something similar again.
Though Sherlock was impatient to solve the case, he agreed that the reactions of the police force were most interesting.
Perhaps it would not be such a bad idea.

I love the Baker Street Irregular and I think it's sad they got cut out of Sherlock so here they are. I might add more stories to this but I don't know yet, it might just be a casual thing here and there but unless its in high demand I doubt this will be updated regularly.

I created the character of Mira not as a romantic interest for Sherlock but just so I could give the kids a "Mum" in order to freak out Donovan and Lestrade XD