Jean Fritz! They're clever and have great illustrations and the history is very good. They were my very favorite books when I was a kid.
For a read-aloud, I love the Genevieve Foster books. They are really, really good... with the exception that they are also very old. Some of the language is very outdated. Though they present different cultures evenly and respectfully, they also use words like "Negro" and every once and a while mention a stereotype that you might wish not to pass along. I've read them out loud, though, and have found it very easy to edit the offending bits out. I would just read a chapter ahead and see if there's anything you'd like to avoid. For the most part, there isn't... but if you'd rather not be caught off guard explaining what a "Red Indian" is then forewarned is forearmed.
For books for him to explore, the "If You Lived..." series is very good, too. I think they may mostly concentrate on US history, though.
And there's always Magic Treehouse. But they suck in their own, special way
I'm also dubious about their historical accuracy, though I have to admit that I haven't actually read them so that's just my own bias. I've heard that the study guides are really good. I do approve of the Magic Treehouse series for building reading fluency, if that's something you'd like to work on. They're great for that.