Sunny Side Up (Sunny, Book 1) / Holm, Jennifer L.

Sunny Lewin has been packed off to Florida to live with her grandfather for the summer.  At first she thought Florida might be fun -- it is  the home of Disney World, after all.  But the place where Gramps lives is no amusement park.  It’s full of . . . old people.  Really old people.
 
Luckily, Sunny isn’t the only kid around.  She meets Buzz, a boy who is completely obsessed with comic books, and soon they’re having adventures of their own: facing off against golfball-eating alligators, runaway cats, and mysteriously disappearing neighbors.  But the question remains -- why is Sunny down in Florida in the first place?  The answer lies in a family secret that won’t be secret to Sunny much longer. . .