Hi, sittin pretty!

I'm with you about nice "boy" books not filled with potty humour and so on--hard-ish to find.

These are not the nonfiction books for which you asked (I'll give that a think), but some fiction books at more or less the reading level I think you're seeking and which I've found very appealing to my boys (4, 6, & 8) are:

1) Esther Averill's Cat Club series (the most boylike ones are The Hotel Cat, Captains of the City Streets, and Jenny Goes to Sea, I'd say, but they're all good): this is a lovely series of short-ish chapter books (about 120 pages, picturesquely illustrated, with nice big print) from the 1950s. Several cats have a club, with lots of meetings (all conducted in a very orderly fashion!) and subsequent adventures. There are some humans, but they are mostly around the fringes of the stories; the heroine cat is Jenny, but she has brothers and male friends, who generally get large chunks of the action, too. What Frenchie (my husband) and I love about these books, apart from the general air of fun, is the tone: the cats are all terribly polite to one another, and are greatly concerned both with decorum and with the effect of their actions on others. It seems strange to say this about talking animal books, but if I had to pick one adjective to describe the series, I'd say they were genteel. (published by the New York Review of Books)

2) Clever Polly and the Stupid Wolf by Catherine Storr has been a big hit here; a wolf wants to eat a little girl, who outsmarts him repeatedly. He has many fantastical schemes for getting her in his clutches (think Wile E. Coyote), but she is far too clever to let herself be caught. Despite the female protagonist, this is a particular favourite with my lads. (published by Jane Nissen Books)

3) The Great Piratical Rumbustification and The Librarian and the Robbers, by Margaret Mahy, with pictures by Quentin Blake. Very short (I'd say more short story length than chapter book, although they are divided up into chapters), and very witty. In the first one, three children are left with a babysitter who turns out to be a pirate, who promptly throws a big party for other pirates at the children's house. Mayhem ensues, but all turns out for the best. Funny and a bit zany. In the second, a librarian is kidnapped by villains, who are converted to good guys by literature and a good woman--gotta love that! (published by David Godine)

For a couple of excellent boy read-alouds for that age (I'd say they're about grade 5 or 6 reading level? I'm not good at estimating that sort of thing), try Philippa Pearce, especially Minnow on the Say (perfection!) and Tom's Midnight Garden. They're Puffins from the '50s, but are still in print. In Minnow on the Say, two boys (who seem to be elevenish or so) spend their summer in a canoe, seeking clues to an old family mystery involving hidden treasure, the finding of which will enable the older boy's family to stay in their ancestral home. Really wonderful--the zenith of boys' books! In Tom's Midnight Garden, the hero is sent away to stay with an aunt while the rest of his family is in quarantine (measles or some such); the aunt's house turns out to be magic, and he has time-travel adventures of a gentle and touching sort. Very good indeed.

Hope some of those will appeal--