This character doesn't even have a name. He's the boy who's only 0.58 there, and he comes from the region of averages. Milo meets him partway up the stairway to infinity. Confused yet? Don't worry.
Although they don't talk for long, the boy has some important things to say to Milo about the importance of learning and seeing things differently:
"[O]ne of the nicest things about mathematics, or anything else you might care to learn, is that many of the things which can never be, often are. You see," he went on, "it's very much like your trying to reach Infinity. You know that it's there, but you just don't know where – but just because you can never reach it doesn't mean that it's not worth looking for." (16.22)
What a nice sentiment. And the more we think about it, the smarter it sounds. The little boy has so much assurance that it is "worth looking for" the things we "can never reach." He has complete faith in his own ideas, even though he doesn't even have a whole body. He may look like he only has 0.58 of a brain, but he sure talks like he has a full one – maybe two!
These profound philosophical ideas coming from a young kid makes us think of Alec, the other little boy Milo meets in the Lands Beyond. Maybe the 0.58 child and Alec are able to teach Milo such valuable ideas because they're kids: Milo's more likely to listen to someone his own age than to a grown-up. Although they're some of the youngest characters, the 0.58 child and Alec say some of the wisest things in the whole darn book.