Some that my daughter liked at about that age (she's now 10, and her reading level matches your description):
The Unintentional Adventures of the Bland Sisters by Kara Lareau (a 3-book series)

The Unicorn Rescue Society series by Adam Gidwitz and a bunch of co-authors

But even in 1966, steamships were rapidly being replaced by diesel-powered ships. I guess language and mapmakers hadn't caught up yet.

Note the label on the red line? "Steamship Routes." Turns out the map is older than I thought, 1966 (it's in much better shape than the other one, which is two years newer).

And of course, it's still there. Over 50 years after the map went out of date. I don't think I've taught using an actual physical map since about 2007, and I'm betting my colleagues haven't either. But I don't think it's going to be removed any time soon.

What's really weird, though, is that the building was completed in 1981. So that means that someone decided to install a map that was out of date 10 years before into a brand-new classroom. I really wonder what the thinking there was.

It is, in fact, dated 1968. Which means that just three years later, it was already seriously out of date. Egypt was Egypt again, Bangladesh was no longer part of Pakistan, and Trucial Oman had become the UAE.

Part of it is placing it in time, along the lines of the XKCD date a world map flowchart. xkcd.com/1688/

There is, at most a 10-year window that it could have been made (Egypt, but not Syria, being labeled "United Arab Republic" pins it to 1961-1971.