So, this was something I wrote a few months ago for a tumblr prompt. Basically, the prompt was for a big/little!au - with Anna being the big sister and Elsa being the little sister - and how Elsa would react to finding out that soon she would have to share Anna and Kristoff with a new baby.

"Elsa. Can you- would you come sit by me for a minute? There's something we'd like to talk to you about."

The eight year old looked up from her place at the small desk in the corner and slowly turned around in her chair to face her big sister. Anna was sitting on the nearby couch, Kristoff - Elsa's new brother in law - sat just beside.

"Am I in trouble?" she asked, standing and wringing her hands nervously. "I-I know I forgot to feed my fish before school, but I fed him as soon as I got home, I promise! He's okay."

"Wha... Elsa, no." Anna got up and wrapped her arm around the girl's shoulders and led her back to the couch, seating her between herself and Kristoff. "No. You're not in trouble, not for the fish or for anything else."

Elsa looked back and forth between the two adults for what seemed like hours, anxiously waiting for one of them to say something. If she wasn't in trouble, then what was this all about? They both wore almost pained expressions, so clearly it was important, whatever it was. And the longer they made her wait to find out, the more her brain churned with ideas about what could be going on.

Maybe Kristoff ate the last of my birthday cake and he's afraid to tell me because he promised that he wouldn't. Or... or maybe ANNA ate my cake! She loves chocolate almost as much as I do... but... no, she wouldn't do that.

Maybe since I'm getting bigger, they're going to make me do more chores... I hope I won't have to clean up Sven's poop in the back yard. She shuddered. Gross.

...Maybe they want to talk some more about how much time I spend in my room and how I need to make more friends. ...I have friends. She scrunched up her little face into a scowl. Sven is my friend... even if he is a dog. And Olaf! Olaf is... well, Olaf is a stuffed snowman.

She still remembered the day Anna and Kristoff had given him to her; they'd just unpacked everything from her room from the old house. After Mama and Papa died Anna couldn't afford to keep the big house anymore and they had to move to a new house... a smaller house. Too small for Kai and Gerda to come, too, little houses didn't need housekeepers or butlers. And "yes, too small for your pony" Anna had replied sadly when she tucked a crying Elsa into bed that first night. "But it is the perfect size for Olaf" she said as she placed the new toy into her sister's arms, hoping he'd be a comfort to her. And he was.

She loved Olaf... but she still hated moving.

I don't want to move again! The thought was irrational, she knew, there was no reason to think this talk had anything to do with that, but that didn't stop the panic from settling into her gut. I finally started to like it here!

Neither of the pair seemed to notice the distress of the girl nestled between them, both too focused on one another, exchanging in a silent debate of raised brows, bulging eyes and head gestures, each trying to urge the other to be the one to speak up and get it over with.

If Elsa hadn't been so stressed, she'd have laughed at the way their heads were bobbing around like chickens.

And then it hit her - the worst thought imaginable.

Oh no. No. Please. Not that. Anything but that.

She took a deep breath and held it, trying to tamp down her fears and slow the pounding of her racing heart. "Is... um..." Her voice shook, as if it knew she didn't want to ask such a question - one she wasn't sure she wanted to hear the answer to. But she had to ask; she had to know. "Is one of you... sick? A-are you going to die?"

"Die?" Kristoff all but choked out. "Elsa, why..." he shook his head, more shocked and concerned about the girl's train of thought than anything, "why would you think one of us is going to die?"

"I don't-" Elsa shook her head, swallowing hard. "I don't know. You guys are just acting really weird and I-I just thought... I already lost Mama and Papa and I... I don't want t-"

"Oh, Elsa." Anna swooped in and pulled her baby sister to her chest. She pressed a kiss to the crown of blonde hair, letting her lips linger for a moment before turning her cheek to rest on the spot. "Honey, nobody else is dying, alright? Not now, not ever if I have any say in it."

"But... you can't... everybody-" Elsa argued, her protests muffled by the fabric at Anna's chest.

"Let's just... let's talk about something else, okay?" She tipped the younger girl's chin up so she could see her face, her heart clenched at the sight of Elsa's already reddening eyes and her flushed, damp cheeks. While softly wiping away the tears, Anna smiled down at her, "no more crying, okay? ...Unless they're happy tears." She tapped Elsa's nose, earning her a small giggle and a nod. "Here," Anna said, releasing her as she reached across to the coffee table, retrieving a small envelope, "I want to show you something."

Carefully, Anna withdrew the contents of the packet: a small stack of paper that looked to Elsa like some odd sort of photographs, black and white and kind of fuzzy. She leaned closer to get a better look.

"Do you know what these are?"

Elsa shook her head.

Anna handed her the photos. "What do you see?"

"I'm supposed to see something?" She studied them curiously. "Is this like one of those 'Where's Waldo?' pictures?"

Anna laughed, "no, no... not exactly, but... well... there is a person there." She leaned in close, snuggling into her sister's side. "Do you see the face?"

Elsa stared for a minute, then: "It's bald."

Now Kristoff was laughing too. "Babies usually are, Kid."

"Waldo is a baby?"

Kristoff snorted. "Waldo Bjorgman, what'cha think, Anna? Kinda has a ring to it, no?" His wife's glare wiped the grin off his face. "Okay. No."

"Elsa, I'm... I'm pregnant." Anna beamed. "Kristoff and I are having a baby." She took her little sister's hand in hers. "WE - our family - we're having a baby."

One of Elsa's brows rose up towards her bangs. "That's it?"

Anna and Kristoff exchanged a puzzled glance. "Yes?"

"Okay."

"Elsa, you're going to be an aunt," Anna laid her hands on her belly proudly, "isn't that exciting?"

"Sure."

Unconvinced, Anna worried her bottom lip between her teeth, she'd been afraid of Elsa taking the news poorly. After their parents deaths, Elsa had clung even tighter to her big sister and though she didn't always show it, Anna knew how much the girl loved the attention the couple showered her with. They were all she had and now, and with a new baby coming, she would have to share them. And after Elsa's little breakdown about fearing she'd lose them...

Anna sighed. "It's going to be okay, Els, I promise."

"I know."

"Kristoff and I love you SO MUCH-"

Elsa smiled. "I know."

"-and that's not going to change, okay? I promise."

"Okay, Anna."

"We just want you to be happy."

"I am happy."

"And if- wait, what? You... you are?"

"Yes." Elsa put her hand on Anna's knee and gave it a pat. "Are YOU happy?"

Anna's face lit up at the chance to gush about her pregnancy. "I'm very happy! More than happy, I'm thrilled. Ecstatic."

Elsa laughed. "Then why are you crying, silly?"

"I'm not crying." Anna wiped her face with her sleeve and sniffled. And at the 'see I told you so' look from her sister: "Fine, I'm crying."

"Hormones." Kristoff grumbled.

"I was just a little worried, I guess."

"Don't worry, Anna," Elsa grabbed her hand, "you'll be a good mom.'

"That's not wha- Y-you really think so?"

"Of course. You've been a good one to me, since..." Elsa looked away, "well, you know."

Anna nodded; she did know. She had loved their mama so much, as had Elsa, so knowing that her little sister thought she even came close... that meant a lot. "I had a good teacher."

Elsa nodded. "I miss her."

Anna hugged her tight, pulling her flush against her side. "I miss her, too. And Papa."

"And Papa," Elsa agreed.

Kristoff reached his arm around Elsa and over to Anna, massaging her shoulder. He didn't need to say anything, just being there for her was enough. He kept her sane and calm and gave her love when her world came crashing down, or like now, when she just needed some support. He was her rock.

"I don't know how to be an aunt." Elsa announced after a while, almost disappointed. "I didn't have a teacher. What if I'm bad at it? What if the baby doesn't like me?"

"Don't you worry about that, Cupcake." Kristoff chimed in. "You already know how to be a sister, right?" Elsa nodded. "Well... think of it kind of like that. You will be the baby's aunt, but you and the baby are going to grow up together, just like you and Anna. You'll be like it's sister. Only, this time, you'd get to be like the BIG sister. Would you like that?"

Elsa grinned and turned her attention to Anna, who was also smiling ear-to-ear... as well as a little misty-eyed with fresh tears. She never ceased to be thankful that she had found such a good man, one who accepted her little sister and agreed to help raise her practically as his own. He truly loved Elsa and for that she couldn't help but shed a tear or two. (But, if you asked her, she'd blame them on the hormones.) Kristoff would be a good dad and according to Elsa, she would be a good mother.

"Anna?"

"Hm?"

"I may not have had someone to teach me how to be an aunt, but..." she bit her lip, "I did have someone to teach me how to be a big sister."

Anna grinned, tucking some stray hairs behind Elsa's ear.

"A great one."

"...Thanks, Els."

"Anna?"

"Yes?"

"If I sneak Waldo to the kitchen to eat chocolate... would you be mad at me?"

"Elsa, the baby's name is not Waldo."

Elsa shrugged.

"And I guess I can't be mad at you for passing along family traditions, can I?" Anna winked, giving her shoulders a playful shake.

Elsa shook her head happily. "Nope!" Suddenly, with all the energy of an eight year old, she jumped off the couch and grabbed Anna's hand, pulling her towards the kitchen. "I think it's time for some family tradition-ing right now!"

"Elsa, it's almost bedtime!"

"Come on, Anna. Waldo's hungry!" she teased, bringing her hands up to her mouth, as if she could stuff back in the fit of giggles that were pouring out.

"Elsa!"

Suddenly, they were in a showdown, both girls facing the other, neither moving but both ready to take off at any moment. The seconds ticked by as the sisters stared each other down, then, Anna cracked. The smirk that crept onto her face made Elsa's stomach drop... she knew that look. If Anna caught her, they'd wind up a tangled mess on the ground, Elsa writhing on the floor as her sister tickled her mercilessly, not stopping until she cried.

Not Elsa's idea of fun. No, she won't catch me. Not today.

There was only one thing left to do... It was now or never.

Elsa side-stepped, inching closer to where she wanted to go, Anna balancing out her moves just feet away. When she was within reach, she flung open the cabinet door, snatching out a bar of chocolate and waving it tauntingly in Anna's direction before taking off out of the kitchen, down the hall and into the safety of her bedroom. Leaning against the closed door, Elsa unwrapped and bit into her treasure. She couldn't help the satisfied "mmm" that slipped from her lips.

On the other side of the door, she heard Anna whimper. And it was just too tempting not to tease her big sister.

"Mmm, this chocolate is delicious!"

"Elsaaa," Anna pouted. "Don't you know it's mean to withhold food from a pregnant lady?"

"I'll share with Waldo!" she called through the door, snickering to herself when she heard Anna's low growl.

"You are SUCH a stinker!"

Elsa opened the door, standing there with a grin on her chocolatey face, holding the rest of the bar out to her sister. "But I learned from the best."