How did Maniac keep Russell and Piper from running away?
Maniac Magee first had to convince Russell and Piper that he wasn't a cop. With that accomplished, Maniac discovered where the two boys were plotting to run away to. Russell and Piper were planning on heading down to Mexico. Maniac's response was first and foremost not utter shock or disbelief. Maniac responded in a manner that told Russell and Piper that he didn't think it was a bad idea. Maniac knows it's a bad idea, but he doesn't let that show.
"Well," he said, "it's good and warm down there, but it's pretty far, you know."
That calm response of Maniac's is what allows his next two bribes to work on the boys. They are not suspicious of Maniac anymore. First, he explains that he is a pizza delivery boy and that Piper and Russel have been chosen to receive a free pizza. The boys have been out all night and are very hungry. His promise of free food is super tempting.
"I'm" -- and with only a moment's pause, the story came to him -- "a pizza delivery boy. We have a contest every week, and you two were chosen for a free pizza."
The two gaped at each ocher. "We were.'"
"Yep. A large."
"Where is it?" demanded Russell, glancing around.
"At Cobble's Corner. You have twenty-four hours to claim your prize."
With a promise of food and no reason to be suspicious of Maniac, Piper and Russell dive right into his next suggestion -- coming back with Maniac in order to learn about a shortcut to Mexico.
He figured he'd better help them make up their minds. "You know," he said, "you're taking the long way to Mexico. If you come back to Two Mills with me, I'll show you a shortcut."
That did it. Soon the three of them were trekking past the Washington Memorial Chapel, Russell and Piper with their bag, Maniac with his satchel.
Basically, Maniac bribed them with food and the promise of valuable intel.