This is a repost of a fic from early 2016, from AO3.
"Here?"
Frisk nodded. They had a blanket under one arm already. Clearly, they were intending to do what they had asked.
"Did you ask those two skeleton brothers?"
Frisk nodded. But Papyrus had thought it wasn't a good idea… not with Undyne lurking around, ready to smite Frisk.
Grillby turned from putting glasses back on the shelf. They looked down to Frisk in a pink tutu, looking innocent and adorable.
"And when you left to come here, I assume you gave up another bed?"
Frisk nodded again.
"The only place you have left is here." Grillby sighed, causing his flames to rise up a little bit. "Sure. Take a booth. Do you need a glass of water? Because I'll show you the tap in the kitchen."
But Frisk was already setting up a booth bed as he talked. Grillby merely waited, polishing down counters and tables, until Frisk seemed to get restless. Before long, they were sitting up and watching him clean the table.
"…Are you bored? If you're bored and staying here, I will put you to work."
However, Frisk seemed to jump at the idea rather than fall back into sleep, so they were given the task of sweeping up the room, told to watch Grillby lest the straw of the broom catch on fire. They ran around the room, too quickly to genuinely get any dirt and dog hair off the floor, but enough to make a difference. Grillby watched them, and while he couldn't smile, felt happier seeing this young child have a good time.
By the time they were both done cleaning up, Frisk seemed exhausted, and Grillby set them up in one of the booths.
They nodded off to sleep in a matter of minutes, and Grillby sat there, watching them as their stomach raised and lowered with breathing.
Shutting off the lights in the main bar, he decided to stay downstairs, just in case some monster found their way in and had the intent to hurt the young child who was so peacefully sleeping.
After a few minutes, he too was asleep, his flames dying down slightly and his body sliding down in the seat as he got more comfortable.
Frisk turned over with a content hum, and neither of them moved for the rest of the night.
Morning brought a slightly sore back. Grillby stretched once, twice, three times as he saw Frisk come out of the kitchen with a glass of water in hand.
The two nodded to each other and Grillby got up to find something. He must have something for the human child to eat, right?
Eventually getting some oatmeal up, they ate together and he sent Frisk off, Sans coming up to the bar as Frisk walked in the other direction.
"Hey, kid," he said, his grin almost getting larger as Frisk walked by. "Papyrus asked if you want to get together again as friends soon! After you meet Undyne, of course… you guys could probably be friends…"
The conversation continued, but Grillby stopped listening. Heaving a sigh, he felt his fire flare up a little bit, in an attempt to get the sleep out of his body. He had a lunch menu to prepare after his morning chat with Sans.
"Thanks for watching the kid last night," he said, coming next to him.
"…The oatmeal's on your tab."