Siblings, Action & Adventure, Humor, Fantasy & Magic, Heroes -- Fiction. Time travel -- Fiction. Children's stories 

Max Silver. Ordinary eleven year-old by day. Superhero by, um, afternoon. His sister Tiffany Silver has just joined forces with him as Maximum Girl. But are two superheroes too much for one family?They call me Maximum Boy. It's a stupid name, I know, but they started calling me that in the newspapers. And now it's on my costume, so I'm stuck with it...Super-Sibling Rivalry! Ever since Max Silver's sister Tiffany got her own superpowers, she's been flaunting them all over the place. All she seems to care about is her costume,her cool name, and whether her superpowers can make her more popular. Max knows she's putting the whole family in jeopardy by risking exposure. But Tiffany just can't resist showing off for her friends...and beating the school record for the high jump. - from Amzon