Maniac has it tough. It's awfully hard to remain innocent when you leave the only family you've ever known at age 11 and live by your wits for most of the next two years. At the same time, even though he's experienced some really hard times, he has more innocence than we'd expect. But we don't mean innocent like he doesn't get dirty jokes (although he probably wouldn't). His innocence is the inability to see the worst in people and in his willingness to befriend just about anyone. Most of all, Maniac Magee shows Maniac's innocence in his deep-down, can't-be-overcome, wholehearted desire to find a family of his own.
Maniac's innocence often puts him in danger. His inability to grasp just why people didn't want him in the East End, or exactly what was going on in the McNab house leaves him vulnerable to the hatred of others.
Maniac stays with Russell and Piper because he understands that innocence can be lost—but it can also be saved.