Inspired by littleoldme's Mommy Anita Challenge.
One or more Buffyverse characters is sucked somehow into the Serenity/Firefly 'verse. As a side effect of whatever brought them there, they're turned into a small child. Now the crew of Serenity has to deal with having a child/children on board!
Just think how much Mal would freak at a child calling him Daddy! And the fun that "Uncle Jayne" could have. Plus, I can see River really bonding with a kid, especially if you chose Willow, Faith, Buffy, or Dawn and gave them powers.
Bonus for using these characters: