A little one-shot that popped into my head while watching Despicable Me. Enjoy!
The Winchesters had been hunting a fairly smart rakshasa that kidnapped its victims instead of outright killing them. If Sam and Dean had been just a second earlier then they could've saved the little girls parents. They had quickly rushed the girl off to their motel room as this particular rakshasa seemed to prefer children and the only other person to escape had been found brutally murdered the next day. Hence why Dean was now summoning (yelling at) Castiel to come and help.
"Hello Dean. Sam." Castiel said, greeting the Winchesters before noticing that Sam was trying to coax a young child out from under the bedside table.
"Why is there a child here? I was not aware that you had kids Dean."
"We saved this girl from the rakshasha we're hunting. And why'd you assume she'd be mine?" Dean stated, sounding indignant.
"Why is she hiding away from you?" Castiel questioned, drawing closer to the frightened child.
"Two strange men bursting through the door and shooting guns at the hideous creature that just tried to kidnapped you and your parents, then being taken to a crappy motel by the aforementioned men would be enough to terrify anyone, much less a six year old." Dean explained, not caring about the amount of sarcasm he used.
"Oh."
"So could you just stay here and watch the girl while Sam and I go try and find the rakshasha before it ki...gets hungry." Dean quickly censored, remembering about the kid.
"Okay. I will stay and watch the child. Do you know her name?"
"Umm, no. The only thing that she's done besides hide is scream. So won't talk at all." After a few minutes of awkward silence Sam came up beside Dean and shrugged helplessly, the girl still stubbornly hiding.
"Well we're going to go now. We should be back by nightfall. Call if you need any help." Dean said as he walked out the door, Sam trailing behind him. That left just Castiel and the girl alone in the motel room. As soon as the brothers had left, Castiel went and kneeled down in front of the child.
"Hello there little one. My name is Castiel and I am an angel of The Lord. What is your name?"
"Addison." Came the faint reply.
"It's nice to meet you Addison. Would you like to come out of there?" Castiel said holding out a hand to the child. Timidly she grabbed it before crawling out. Not really even thinking about it Castiel scooped her up and set her down on the closest bed before sitting down beside her. After awhile of sitting in silence the child finally asked one of the questions that had been bugging her.
"Are you really an angel?"
"Yes I am."
"Oh. Momma says that angels have wings and funny circle thingys around their heads. Do you have those? She also said angels watch over us. Are you watching over me?"
"The funny circle thingys are called halos. And yes I do have wings and a halo but I only wear it for important meetings and you can't see my wings because they're invisible. I am watching over you until Sam and Dean bring your parents back." Castiel replied.
"You promise that they'll bring Momma and Daddy home?"
"I promise."
"Pinky promise?" Addison asked sticking out her pinky.
"Why would my pinky need to promise? It can not talk to make a promise." Castiel stated, tilting his head to the side as he stared, perplexed as to why the child was offering him her pinky.
"A pinky promise can't be broken."
"Why not?"
"Because the rules say it can't!" The child said like it explained everything.
"Ah." Castiel said, nodding sagely. "How do you make a pinky promise?"
"Well you hook your pinkies together." As she said this, Addison grabbed Castiel's hand and wrapped her pinky around his.
"And then you say I pinky promise with whatever you promise."
"Ok. I pinky promise that the Winchesters will bring your parents home." As Castiel finished speaking the girl launched herself at Cas and hugged him. Automatically Castiel's arms wrapped around the child.
"Thank-you!" She mumbled into Castiel's shirt. Pulling away she looked up at Cas.
"Let's play!"
Several hours later the brothers returned with the shaken, but otherwise unharmed parents. Nothing could have prepared them for what they saw when the walked into the room. Toys littered across the floor, there was paint smeared on the walls and stick figure pictures on the table. On the bed Castiel and Addison were asleep, Addison snuggled on top of Cas and Cas holding her protectively. They were both covered in paint and had small smiles still on their faces. Sam immediately pulled out his phone and snapped several pictures of the two before Castiel stirred.
"Whaa?" He muttered before snapping awake and scanning for threats. When he saw the brothers and the adults behind them he relaxed before gently shaking Addison awake. Bleary eyes blinked up at him before snapping to the door. Seeing her parents caused her to squeal before leaping off the bed and running to them.
"Thank-you for saving us." The father said even as tears gathered in his eyes at being reunited with his family. As the family turned to leave Addison ran back and hugged Castiel's legs. "Thank-you for keeping your pinky promise ."
"You are most welcome little one."
"Will you come play with me again?" "I will try to." With that the small family left the motel and Cas went back to were he was staying, vowing to check up on Addison every so often.
A few weeks later...
As Addison went to bed she thought about her and if she'd every see him again. She was starting to doubt it until she saw the stuffy on the bed. It was a small angel wearing a trench coat with two fuzzy black wings protruding out the back. Hugging the stuffy to her she had the best sleep she'd ever had. Up in heaven Castiel smiled at the dream the child was having.
"I pinky promise we will see each other again."