There are six books in the series, although the inner dust cover hints at a seventh X-Men book, which I have not seen. They're written in simple storybook style with short, easy to read sentences and lots of large and colorful art. They hew pretty closely to the old school origin stories of Marvel's flagship characters (much more so than the current comics!), which of course is always a good thing.
the Hildebrandt brothers (or the Brothers Hildebrandt, as they preferred to be called).
So far the only place I've seen these is at Target, but then again I haven't been anywhere else for a while (I'm quite busy with my duties as President and CEO of Bob Canada's Blogworld) so it's entirely possible other stores may carry them.