Author's Note: Sorry in advance. Based off of a prompt wherein Elsa is a construction worker: I took it in a different direction.
Lingering Promises
Idunn pushed open the door and stepped inside. As was usually the case, her daughter's room looked like the aftermath of a fierce battle, fought not with guns and swords but dolls and blankets and coloring books. Strewn about the mess were pencils and blocks and clothes both dirty and clean, making the terrain treacherous for even the most sure-footed of adventurers. The queen, though hardly that type, could spy an opening when she saw one, and so she took it.
Idunn concealed a groan behind a cough as she sank to the small patch of open floor with as much grace as was possible with her heavily swollen belly. Beside her, her daughter was holding two sticks together and glaring at them. She puffed up her cheeks and shut her eyes tightly, her little face scrunched up in total concentration. A small pile of twigs was lying in front of her, dripping sweet smelling sap onto the carpet and likely to stain it. The queen shook her head and patted Elsa's back when the girl's face, usually a beautiful porcelain shade, began to transition to something more akin to plum. "Elsa, sweetie, time to breathe."
The girl blew out a frustrated breath and dropped her hands to her side. "This is HARD!"
Idunn chuckled as she stroked Elsa's hair. "Can I help?"
Elsa lifted the twigs again and pushed them into her mother's hands. "Hold."
She accepted the gift without comment, watching as her daughter picked up another pair of sticks and brought them together in what seemed like a practiced motion: a quick glance around revealed several more twigs lying about, some of them concealed under other detritus. Idunn suspected that this was the reason the maid had happily informed her that the little princess had been quiet all morning, but like most mothers, the claim that their toddler had been "quiet" was cause for immediate suspicion.
Elsa's angry cry was followed quickly by another offering of twigs. It looked like she'd run out of them soon. "Hold," she muttered, distracted by a new set. Idunn took the opportunity to quietly put the sticks to the side.
"Hold…what, Elsa?" she said in an expectant tone.
"Hold…please," the girl answered, glancing guiltily up at her mother and then back at her work. Idunn smiled and shifted a bit closer. "Very good." She dropped a kiss on her hair.
At the gesture, a swirl of magic appeared, and both of them gasped: Elsa in wonder and delight, and Idunn in nervous awe. The twigs, pushed together at right angles, were now joined at the ends by a thick smear of ice. Lines of frost were drawn down the length of the sticks until they reached Elsa's hands, which Idunn knew not to touch now, lest she be hurt.
She leaned back slightly, her hand falling off Elsa's shoulder and swallowed as Elsa squirmed and squealed and then suddenly thrust the sticks at her face. "Look!"
Idunn gave her a tight smile before carefully taking the new arrangement of ice and wood. In defiance of normal behavior, the ice showed no signs of melting; indeed, if she examined Elsa's creation closely, she could see it pulsing with an inner cold that made something inside of her tremble.
"Elsa…" she said, and paused while the girl shook with excitement. She tried again. "Elsa…what exactly are you doing with this?"
"I'm making!" the girl announced. She had already picked up another pair of twigs, emboldened by her recent success, and Idunn sat silently as the newest pair began crackling as ice raced up their lengths, Elsa's breathless giggles following it as it went.
Idunn said nothing until the magic was finished and Elsa was pressing the creation into her hands with a distracted movement, already intent on the next set. "All right," the queen said, "so you're making…what are you making?"
"Rockaby," Elsa muttered, twisting a stick around in her hands before discarding it.
"You're making a rockaby?" Idunn asked. She thought for a moment, then added, "a crib?"
Elsa nodded. She'd found a twig that she liked more, because this time a pale blue light twined gently around it and its partner until they, too, were merged into one shape.
"Are you making it for me?"
Elsa shook her head, frowning.
"…are you making it for the baby?"
Elsa's happy grin in response lit up her sky blue eyes the same way her magic did, and it almost made Idunn feel safe. Her daughter, with her peculiar gift, never meant her or anyone else any harm, after all. And yet…
She shoved those thoughts away: her paranoia as a human mother raising a magical child was not sufficient basis to reject Elsa. Even if there had been a few incidents before, with servants tendering hasty resignations before all but fleeing for the hills, leaving the royals scrambling for replacements, even if Elsa's powers were unpredictable both in scope and strength, and even if neither she nor her husband were sure of what to do with their child when a toddler's tantrums took on physical form in the shape of harsh winds and razor sharp spikes: the girl before her was her own, and if Idunn could never quite let her guard down around her, she would, at least, never leave her behind.
She took in the room and an idea came to her mind. "Where are you going to put it?"
Elsa blinked and looked up, the ice dissipating as her eyes followed the same track as her mothers, her eyebrows lifting as realization slowly dawned.
"You might have to clean things a little, first," Idunn offered helpfully. "Otherwise the baby can't stay here, can it?"
Elsa's eyes widened in horror, a response that fascinated her mother. From the moment she had learned of Idunn's pregnancy and the fact that she would have a baby sister or brother soon, Elsa had reacted not with confusion or anger or fear, but with a violent anticipation that manifested in such odd ways, like when she insisted on handfeeding Idunn to make sure the baby ate for an entire month, or made sure to hug and kiss her mother around the shoulders and then around the belly. And now crib-making.
"Can you keep your room clean, for the baby?"
Elsa's protectiveness of her unborn sibling was apparently enough to counteract her messy habits, because the girl's voice was totally sincere when she said, "Yes." She stared into the distance and then back at her mother with such intensity the woman almost flinched. "I will." There was something prophetic about her statement that sent a chill up the queen's spine: for all her immaturity, mystery, and magic, Elsa's eyes were filled with a fire that made Idunn feel entirely out of her depth.
She could only hope her child would not feel the same way. But how would they? Elsa's love was a fierce, wild thing, but with it came her complete acceptance, a rare thing that she bestowed upon very few. If Idunn could be certain of one thing, it was that Elsa, once she gave her love, would never turn away.
She smiled in relief. "Good girl. Let's clean up together, shall we?"