When I was young, 12 maybe, I checked a book out of the local library, reading it several times, which initiated a life long live of post apocalyptic fiction. In the book a young boy about my age lives with a tribe outside the ruins of a large city that might have been Chicago. The tribe is at the hunter gatherer level of technology. And his main weapon is a spear. The city itself is a blast zone/dead zone no one is allowed to go in because it is supposedly radioactive. I don’t remember why but he heads into the dead zone and discovers the radiation is no longer deadly. But living in the ruins are a race of evolved rat beasts that are six feet tall, stand on their hind legs, and are spear wielding. The rat beasts come after him and he has a series of near misses until he escapes the dead zone and is rescued in a big showdown between the human tribe and the rat tribe, being saved by the adults whose rules he defied. The book had large-ish print and excellent pen and ink drawings sprinkled throughout. I went back to the library that I got it from but the destroyed my old library card and no longer have the book. It would have been published in the 1950’s or first part of the 60’s. Any help finding it would be greatly appreciated.