If the grandson has a preference for superheroes, I'd second the later Marvel Family material. Also Hoppy the Marvel Bunny and I've always liked Nedor's Supermouse too. I'd think Sparky Watts would be pretty appealing to a new reader.
Really, ANY of the funny animal and humor books that I've read have been equally good. Fawcett's George Pal's Puppetoons is a particular favorite. Any of the Archie clones would be good and simple to read and Archie himself in the early issues of Pep.
If he likes something more action oriented, try the Fawcett Western books. You know they'll always be wholesome and entertaining. For that matter, ANYTHING post-war from Fawcett will be, and most war-time books too, but you could have the occasional Steamboat-type or "dirty Jap" to contend with.
Most Novelty Press books will be pretty good too. Some occasional war-time stereotypes might pop up, but they were better about that than most companies. The Cadet and Dick Cole are two of my favorites. Speck, Spot, and Sis are fun light reading, as is Candid Charlie. There shouldn't be anything bad in those, especially the latter two.
-Eric
