Disclaimer: I don't claim to own Castle or anything from the series. The lyrics at the end of the fic belong to Josh Groban.

Notes: This came to me the other day at work. Hormones resulting from hearing a baby cry inspired this little drabble. Please note I have no kids of my own, but I've done research for years on my own, so I hope this is at least somewhat accurate. If it's not, my apologies in advance (and if you decide to correct me, just be gentle please!).

AU. Thoughts are NOT in italics, for once. Additional inspiration came from the song "Lullaby" by Josh Groban and Ladysmith Black Mambazo.

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Rating for this chapter: K

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For once, it was the high pitched shriek emitting from the baby monitor that woke Kate Beckett up from her deep sleep and not a nightmare. She'd had more than her fair share of them in the last couple of years, but she would take being awoken from an exhausted sleep by an infant over waking up from a night terror any day.

Kate rubbed the sleep from her tired eyes as she turned the baby monitor face down on the nightstand and swung her legs out of bed. She grabbed wearily for her robe on the nearby chair, missing it a couple of times before she managed to snag the soft flannel and pull it over her shoulders. She padded out of the bedroom and into the room next to hers. Only a nightlight was on, but it was enough light to see the squalling infant squirming on her back in her crib.

Picking her daughter up, Kate checked for a messy diaper and saw that she was clean. Alright, maybe she was just hungry. Kate sat them both down gently in the rocker in the corner before inserting her feeding cushion under the arm holding her daughter. With her free hand she opened her robe enough to undo the flap on her nursing bra. She held her daughter to her breast, but the infant didn't latch on, continuing to cry instead. Okay so maybe she wasn't hungry either. What could be wrong?

Kate settled her fussing daughter on her shoulder as she re-adjusted her attire and walked them both out to the kitchen. She patted the newborn gently on her back, alternating between that and rubbing in what Kate hoped was a soothing motion. Around and around the kitchen Kate paced, expanding out to the living room a few minutes later as the baby continued to fuss, albeit not quite as loudly as before.

Kate was running out of ideas when a thought occurred to her. Thinking back to one of her favourite songs as a child, she bent her head closer to her daughter's and started to hum a quiet tune. Thankfully, within moments her little one began to calm down, and Kate continued her pacing.

She'd done perhaps a dozen slow laps around the living area of the apartment when she heard the bedroom door open, and a sluggish figure appeared in the office doorway moments later. Kate bit back a smile at seeing how tired he was, so worn out that he hadn't even bothered putting a shirt on before coming out to them. She'd done all the hard work in birthing the little creature she was cradling against her, yes, but Kate knew he'd had to adjust to having an infant in the house again after all these years, and it hadn't been easy change for him either.

"Is she up again?" Rick mumbled as he approached Kate. He bent to give her a quick peck on the lips, then smiled down at the baby in her arms. "What did she want?"

Kate gave a slight shrug, careful to not startle her daughter. Theirdaughter. "I don't know. She wasn't hungry, and she didn't need to be changed. I was walking with her but she didn't start to quiet down until I started to sing. Well, hum."

Rick smiled despite his exhausted state. "Ah, so she just wanted Mommy. Alexis was like that too when she was this age."

"But Meredith wasn't around much," Kate pointed out. "So what happened when Alexis got fussy and wouldn't sleep?"

Rick held his hands out to Kate, and she gently handed the sleepy baby over to him. Their daughter was small, and in Rick's large hands she seemed even tinier. Rick settled her against his bare chest, and Kate felt her heart melt into a puddle at her feet. Rick could be charming, handsome, and occasionally annoying, but when his focus was centred on their little girl, Kate thought she couldn't possibly love him more.

"Well, Meredith wasn't home long enough after Alexis was born for her to form too deep a bond. She stayed with us long to get her figure back, and then once she got that first job offer after Alexis was born, she left. But even when she was home, I was usually the one getting up with Alexis in the middle of the night when she was still small."

"So there was really no big adjustment to having Daddy instead of Mommy?" Kate asked quietly, squashing down her frustration with Rick's ex-wife. The past was the past, and Alexis had turned out fine. There was no point in getting upset about it now.

"Nope." Rick dropped a soft kiss on their daughter's head, and both parents breathed a sigh of relief when she didn't wake up.

"Have you thought of a name for her yet?" Rick asked Kate, who was stifling a yawn.

She waved him off. "No, not yet. I can't think of something that just... seems right. I don't know."

"What about naming her Johanna, after your mother?"

Kate smiled sadly, feeling her longing for her mother even after all these years. "Maybe as a middle name, but I was thinking of something else for her first name."

Rick nodded. "I understand. Well, she can be Baby Castle until we find the right one." Seeing Kate yawn again, Rick slid an arm behind her and started to guide her back to their bedroom. "We should go back to bed, now that this one is sleeping. You look about as dead as I feel, and in case Baby Castle wakes up in a couple of hours again, one of us needs to be conscious."

Kate nodded sleepily. "Agreed." She let him lead her to the nursery they'd built next door to the master bedroom. It had taken up some of the original office space, and both rooms had had to be redesigned with the addition of the nursery, but now they were all side by side, allowing them quick and easy access to their daughter. The layout had been Rick's idea, and Kate loved it.

Rick gently set their daughter down in her crib, then returned to meet Kate in the hallway. She draped her arms around his neck and gave him a sleepy smile, one which was met with a tender kiss, and then another.

"Hey Rick?" Kate asked as they walked back to their bedroom.

"Yeah?"

"What do you think of this for her name?" As Rick reached behind them to close their bedroom door, Kate stood up on her tiptoes to whisper her suggestion into his ear.

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Hush now baby, don't you cry

Rest your wings my butterfly

Peace will come to you in time

And I will sing this lullaby

.

Know that I must leave, my child

That I would stay here by your side

And if you wake before I'm gone

Remember this sweet lullaby