Author's Note: Nebulously set post-season 3. Currently a one-shot, but if there's enough interest I'll hopefully continue it. More of a Swan-Mills/Swan-Mills-Charming family moment than a Swan Queen story, but if I do write more it will get into shippy territory.
The song is Déjame Llorar; Tish Hinojosa performs a lovely version of it, for anyone who wants to give it a listen. It's not technically a lullaby, but I don't think any of my childhood lullabies were actual lullabies, and I think it works. The title of this piece comes from the song. Credit to my roommate for suggesting Tish Hinojosa when I was looking for songs for this story.

"Mom, over here!" Henry called out. Regina was surprised she hadn't noticed them when she came in, but then they were rather difficult to see with their booth in the back corner of Granny's. Odd choice for Emma Swan, Regina thought, she usually likes to see everything. She glanced at her watch. Her first meeting wasn't for another hour; she'd planned to take her coffee to the office and do a little paperwork first, but it was Henry's week with Emma and she couldn't resist the chance to spend a few minutes with him, especially seeing the way he smiled at her.

Emma resisted the urge to turn and watch Regina. She was curious to see how the woman reacted to their son's request. They'd been getting along much better lately, but she suspected the Mayor would never really like her or relish the thought of eating a meal together. Still, she knew Regina missed Henry when he was with her, at least as much as she missed him when he was with Regina, so she wasn't surprised when Regina and her to-go-cup made their way over.

"Good morning Henry," she greeted him with a warm smile. He was already scooting over to make space for her, but she felt it would be impolite to sit without greeting the Sheriff. Still smiling slightly, she turned to the blonde and was surprised to discover the reason for the pair's unusual locale—her sleeping baby brother.

Emma couldn't help but smile at the warmth on Regina's face when she noticed the baby. It was nice seeing that side of her; it helped her remember that this woman loved their son, and despite everything had given him a good life for the ten years before she came along. "Morning Regina," she said warmly, drawing the brown gaze to her own.

"Good morning Emma. Do you mind if I join you?"

"Go ahead," Emma said with a gesture to the spot next to Henry. "We're just waiting on breakfast."

The next few minutes passed pleasantly as Henry told Regina about what he'd done at school the day before, and about the math test he had that day. Emma proudly informed her that he'd gotten every question right when she'd quizzed him last night, and Regina silently admitted that she was impressed with how far the other woman had come as a parent.

When Henry and Emma's food arrived, it took all Regina's self-restraint not to chastise Emma for the cinnamon roll on their son's plate. At least there's fruit, she thought with a sigh, eyeing the small bowl of melon. Just as they started in on their omelets, Regina feeling a bit awkward, baby Charming began to fuss. Emma stopped the fork halfway to her mouth and sighed, putting down what would have been her first bite, and complained, "It's like he knows." Regina couldn't help but smirk.

Regina watched as Emma gently pulled the infant from his carseat and cradled him to her chest. He wasn't crying yet, but she could tell he was on the edge.

"Maybe he's hungry too?" Henry suggested.

"Mary Margaret fed him less than an hour ago," Emma countered, "he shouldn't need anything for a while yet."

Emma began to coo at her brother, but he seemed unimpressed, beginning to cry out-right now. She checked his diaper with one hand and sighed to find it clean and dry. What was it he needed? Even in the memories Regina had created for her, Henry had been older than this, nearly a year, when she'd gotten him back from social services, and it hadn't taken her long to learn his routines and his needs. She loved her parents' new baby, but so far she simply couldn't figure him out, and she was reminded that she'd never really been good with kids except for Henry—and even most of that was made up. Sighing again with a longing glance at her breakfast, Emma stood and began to bounce her brother.

To Emma's great surprise, Regina spoke up. "Here, let me take him," she offered, standing gracefully. Emma looked at her uncertainly; she was inclined to take it as an insult to her parenting—or sistering—skills, but she saw no malice, only a desire to help, and perhaps even a desire to know this new person who'd come into their—whatever they were; not quite a family, but not not a family either.

Emma handed him over gratefully, surprised by the tenderness with which Regina smiled at him even as he continued to squall.

"Well hello little prince," Regina murmured as she brought him to rest against her shoulder, "I see you've been giving your sister a hard time." She began rubbing small circles on the tiny back, and when he continued to cry she began to hum. Emma couldn't help watching, and she smiled to see her brother beginning to calm. With a twinge of regret, she wondered how many times Regina had calmed Henry like that.

As Regina began to sway lightly, eyes drifting nearly shut, her humming turned into a soft lullaby.

Si es un delito amar, delincuente soy
Emma was entranced, her breakfast forgotten.
Por que no eh de pagar, las culpas de mi amor

After a few moments Henry nudged her under the table, bringing her back to herself; she was too amazed by the sight before her to even feel embarrassed, but she did begin eating, eyes flickering back to Regina and the baby a little more often than was strictly appropriate in polite society.

By the time Regina finished her song, Neal was sleeping in her arms. Her smile remained as she returned him to his car seat and gently strapped him in, rubbing his belly for a moment when he shifted in his sleep. Emma quickly returned her eyes to her plate as Regina straightened.

"Well, I should get to the office, and let you two enjoy your breakfast," Regina said calmly, bending to place a gentle kiss on their son's forehead that he accepted with only the faintest flush. As Henry mumbled a soft "Bye Mom," Emma glanced at her again and was surprised to see her features, though still soft, held a hint of sadness now. Had she really missed the kid that much in just a few days without him? Or was it something else?

Emma found her mind lingering on that look long after the door closed behind the brunette and she returned to her meal, and all throughout the day Regina's melody played in her mind.