This is a great story. It centers around two boys who live next door to each other. The main character lives with his aging father and the other boy lives with him mom, the father having left years ago, leaving them somewhat poor. There's a storm coming and a man selling lightning rods for the storm, but with the storm comes a carnival, but not your ordinary tents, freaks and animals. This one only comes every hundred years, and for those lucky few, their deepest and darkest wishes can be granted, but there's a dire price to be paid.
The coolest part is the merry-go-round which goes forward and backwards. If you come back after the carnival closes, you can go backwards and it makes you younger. The protagonist and his friend get caught when the other boy, and I think his last name is Black or Nightshade, is tired of being poor and he wants to be an adult and go forward on the merry go round, and the other boy is trying to stop this from happening because he'll lose his best friend, but the ring master says he's going to send the protagonist backwards and turn him into a diaper wearing toddler. He's already done this to one of his once human minions.
You can see why I like this story. Disney made a movie out of it and you can get it on DVD. I own a copy and it's really well done.