Okay so I have played about a bit with the dates, hope you don't mind too much:
Bellatrix is the oldest
Sirius and Andromeda are a year younger than her
Regulus and Narcissa are two years younger than Bellatrix
I don't own any of the good stuff in here, that all belongs to the wonderful, most revered, JK Rowling!
"Bellatrix Black!" the voice cracked like a whip through the opulent hallway.
In one synchronised movement three young girls turned to stare fiercely at the origin of the voice. All the girls were beautiful, each in their own way. The tallest of the three had long black hair that fell down in untamed curls to the small of her back, her eyes were alert and gave her face a determined glint. The contrast between her pale skin and matt black hair was startling and gave her a mysterious air. However, this contrast was nothing compared to the one between her and the sister who stood by her side. You could definitely tell the girls were sisters yet they looked drastically different. The smaller girl had perfectly styled glossy blonde hair and piercing blue eyes. The two girls both had an aloof and superior air that screamed money and 'good' breeding at anyone who confronted them. The third girl looked similar to her sisters, however she had a much more friendly air about her. Her mousey brown hair hung loosely around her face and her chocolate brown eyes sparkled.
"Hair's getting a bit long isn't?" Bellatrix jeered down the hall at her cousin, a gleeful smile spreading her lips.
"Do you not like it Bella? It's all for you my sweet!" Sirius Black stood before his cousins and bowed to the eldest with a flourish and a cheeky grin.
Bellatrix giggled most uncharacteristically, but her sisters did not look at her agog because if there was one person who could make Bella do anything it was their cousin, Sirius. He was huge for his age standing at over five foot tall just after his eleventh birthday. His hair had grown considerably since Bellatrix had seen him on her Christmas holidays from Hogwarts. He was handsome, but ruggedly so with a mischievous grin and eyes that shone endlessly. He filled the girls with glee and often got them in trouble with their parents for doing 'outrageously unbecoming and silly things!'. not that the girls cared.
"It's horrible! You look like a shaggy dog!" Narcissa interjected a calculating look on her face, "if you just let me…"
"Don't let her go anywhere near you Sirius, have you seen what she did to mine last week!" Regulus, Sirius's younger brother strolled up behind him and gave Narcissa a wary look.
"I did wonder what had happened, I thought you'd had a nasty run in with a Banshee ," Sirius chuckled eliciting more laughter from Bellatrix and Andromeda.
"What do you mean! It's very fashionable! And I'm getting much better at the spell." Narcissa looked disgruntled and folded her arms across her chest.
"Of course, the craftsmanship is incredible, the style just isn't to our liking is it, Reg?" Sirius quickly reassured his youngest cousin.
"No, not particularly."
"Anyways, that doesn't matter now, it'll grow out in no time, I'm sure Reggie. Have you seen the snow, Sirius!" Bellatrix started to bounce on the balls of her feet as Narcissa and Andromeda pulled on a pair of exquisite cloaks.
"Have I seen the snow, of course I've seen the snow!" Sirius clapped his hands together and winked at Regulus.
"We waited for you two before we went into the garden, the snow is still fresh." Andromeda said throwing the boys thick pairs of dragon skin gloves perfect for this kind of weather.
"Good good, come on then!" Regulus, Andromeda and Sirius began to move towards the back door that lead into the Blacks ample garden.
"Wait Cissy needs a scarf!" Bella shouted giving her sister a stern look.
"Bella, come on!" Sirius and Narcissa moaned in unison.
"No I don't want you freezing to death out there…mum and dad would kill me, now go get a scarf."
Narcissa ran through the kitchen to the main house to get her scarf, returning a minute later with a deep green velvet scarf that she wound around her neck looking at her sister pointedly. Bellatrix nodded and led the way into the garden. The snow was deep, reaching their shins and making it difficult to walk. Soon enough their footsteps began to pack it down letting them run around reasonably freely yelling and calling to each other. Andromeda found some huge icicles hanging from the pavilion and they all spent a moment marvelling at how large they were. Sirius and Bellatrix had fun conjuring up horrific stories where young unsuspecting children were skewered, flattened or mutilated by falling icicles to which Narcissa responded with outrage and Andromeda and Regulus fell about laughing. A little while later after the girls had made snow angels and the boys had made fun of them Regulus found a long piece of ice behind the summer house that they began a sliding competition on.
"Argh! Sirius that wasn't fait, I wasn't ready!" Andromeda squealed as she was sent careening down the slope by a hefty push from her eldest cousin.
At the bottom of the incline she landed in a deep snow drift that covered her in a mountain of snow. Her giggles could be heard through the snow at the top of the slight hill. Sirius whooped and followed her down on his stomach closely shadowed by Bellatrix and Regulus, the three of them spinning and sliding madly until they flopped into the snow at the bottom. Narcissa watched with both delight and fear before sitting demurely on her bottom and sliding down neatly. The others laughed at her poise and pelted her with snow as she reached them.
"Hey!" She shrieked and formed herself a snow ball which she very accurately aimed into the face of her eldest cousin.
"That's my girl Cissy," Bella yelled and pulled her up onto her feet, "Come on, Andy, we can take them can't we!"
Andromeda and Narcissa launched into action rolling snow balls as the two boys ran back to a safe distance just behind a low wall. It was all out war, Bellatrix, Andromeda and Narcissa worked together as only close sisters could to create tactical warfare that made the boys quake in their boots. The two brothers used brute force more than tactics to hit the girls and Andromeda had a red mark to prove it. Narcissa had broken three fingernails and Bellatrix' hair was so wet that it no longer moved freely, just stuck to her face and back.
"Hey Sirius, Sirius stop," Bellatrix screamed amid a shower of small, hard snowballs, "Cissy needs to go inside, she's hurt her wrist! Stop! My little sister need to go inside!"
"Sorry, Bells go ahead, take her indoors, but be warned as soon as you come out, IT'S WAR!" Sirius bellowed and then guffawed making the noise echo around them.
Bellatrix moved forward with Narcissa who was clutching her wrist inside her cloak. As the two girls moved forward Sirius peered worriedly at Narcissa. Regulus came up behind Sirius to check on her too. As the two of them opened their mouths to ask if she was okay two huge hunks of snow came from behind and hit the back of their heads. Andromeda's laugh erupted as her sisters brought snowballs out from within their cloaks and pounded the boys from the front. For almost five whole minutes the girls kept the boys trapped in a blizzard of compacted snow as they alternated their attacks. Unfortunately, Sirius broke away from his brother during one of Bella and Cissy's onslaught and tackled Andy sending them both down into the snow in a flurry of cold white fluff.
"ARGHHH!!" Bellatrix let out a feral war scream and ran in to the rescue of her sister whilst Narcissa engaged Regulus in a fierce battle. Bella, Andy and Sirius rolled around in the snow screaming and hurling handfuls of snow at each other whilst their relatives through huge flurries of snow at each other.
After another half an hour the five of them collapsed into a heap under the cover of the pavilion as the snow came down very heavily. Their clothes were drenched and their faces raw, but they still laughed and joked together until Druella called to her daughters.
"Come on inside now girls! Your clothes will get ruined and your father would like to talk to the boys!" And with that she disappeared back inside the house and the cousins made their way back into reality.
This is it for now, however if I ever get inspired it may turn into a story, hope you enjoyed it : )