Written for a prompt on comment_fic: part or all of the Firefly crew gets de-aged to small children
They didn't really know how to handle it. It wasn't even the fact that they were kids, it was that they didn't act like ... them anymore.
Kaylee took to mothering all four of them who got de-aged, and spoiled them rotten of course. Book told them stories in funny voices, and was helpful too. Mal tried to yell at them good when they needed it, but for some reason, they just giggled when he tried to be stern with them.
Wash liked to sit in the pilot chair on top of a stack of boxes to reach the wheel, pretending to be flying the spaceship; he also liked playing with toys a lot. So that was the same, pretty much. The strange thing was, he wanted constant attention... from Mal. He followed Mal around, insisting that they play with his dinosaur toys and that Mal tell him stories and asking Mal question after question. "Why is space so big? What's bigger, space or dinosaurs? How do you know all of space isn't just the mouth of one giant dinosaur? Who would win in a fight, you or a dinosaur? Would the dinosaur spit you out if you tasted funny? How come you won't let me fly the spaceship? When I'm seven, can I fly the spaceship? Why not? Hey, why don't you make a spaceship out of candy? Can I try on a spacesuit? Why are loud things called loud? Shouldn't loud things be called 'Boom'?" and on and on and on. Once, Mal even tried to explain to Wash that when they were bigger, they might not even like each other that much, but Wash started to cry, so Mal gave him a hug and said he was just kidding.
But for all Wash's energy and constant talking, at least he was cheerful and well-behaved. The others weren't nearly so sweet. Zoe was quiet and reserved, and spent all day with a pile of picture books, reading them again and again. She wasn't interested in talking to Mal at all; when Mal tried to joke around with her, or offered her an airplane ride, she was so shy that she didn't even speak, just smiled and hid her face in her sweater and shook her head no. She would sometimes talk to Simon, Mal noticed, only a bit annoyed at her preference, but he figured it was just because Simon bought her more books every time they went to a new planet looking for word of a cure of de-aging. Zoe followed him around the clinic sometimes, and of course Simon didn't have any idea how you're supposed to talk to kids, so he kept telling Zoe boring little details about how the circulatory system works or about the important periods in the history of neo-classical watercolor paintings, but for some reason, little Zoe seemed to like nothing better than learning and reading, so Mal tried not be annoyed that his First Officer didn't have any use for her Captain. Of course, he wasn't too happy when he tried to pry a book out of Zoe's hand to make her go to bed (it was two hours past bedtime!). Zoe still didn't say anything to him, just kicked him in the knee. Hard. Landing on the ground, he yelled at her, threatening to look up the old court martial rules, as she grabbed her book and ran away.
But at least she was quiet. That was something. Inara, on the other hand... Mal never would have believed that she was such a wild child. She had none of the gentility that characterized her as an adult, instead shouting and screaming at the top of her lungs, nonstop, sheerly for the joy of it. She was quite the tomboy, also, which led to a scuffle when Kaylee tried to get her to put on a pretty dress so they could have tea with the dolls that Kaylee had bought, thinking that little Zoe and little Inara would like them. Zoe politely wore the dress and talked to the dolls but obviously didn't much like it. But Inara yelled and screamed and kicked Kaylee in the shins and ripped up the dress so she couldn't be made to put it on. She even knocked over the table and ran out, yelling a bunch of curse words that even adult Inara wouldn't say.
Little Inara didn't ever listen to anyone, and didn't respond to bribes, threats, scoldings, or anything else. She went on a wee reign of terror, climbing on everything in sight, and even inventing a game that the other children enjoyed and that the adults hated: it was called "Hee" and the kids shouted "Hee" every time they got points. It was 5 points for hiding rotten leftovers in an adult's shoe so they stepped in it, 10 points for spilling water on an adults lap so it looked like they wet themself, and 25 points for getting garbage in an adult's hair, whether it was by sneak attack or by aimed projectile. All the children giggled as they played this wretched game, but none snorted their laughter as loudly as little Inara, and none of the other children ever scored as many points. She got fifty points one day just from various foods in Kaylee's shoe. Mal tried not to laugh as he realized that he had never seen sweet-tempered, ever-pleasant Kaylee quite so exasperated with anyone. It was all Kaylee could do to stop herself from yelling at the giggling girl in rage. Of course, Mal didn't find it so amusing when Inara invented a little catapult that sent engine grease flying right at him. He put a stop to that one right away.
The biggest surprise, though, was little Jayne. Mal thought that he would be a terror - he just assumed - but actually Jayne was... sensitive. He got upset at every little thing. He cried ALL the time. The only one who could comfort him was, of all people, the Tam girl. Mal didn't understand it, but River and little Jayne just took to each other, River throwing him up in the air and catching him like he was a playground ball, and Jayne giggling like a madman the whole way. And when Jayne got upset, she would scoop him up and leave, like she wanted to teach him that the words of normal people were properly ignored a good amount of the time. They walked out with Jayne burying his face in her neck and her calmly addressing the crew with the simple explanation of "I like him better this way." It was downright disturbing.
All in all, Mal couldn't wait to find a cure. If he had to go to every backwoods planet in the verse, he'd do it.