The Fall of Constantinople by Bernadine Kielty - a retelling of how Constantinople fell in 1453. Out of print, so difficult to buy, but it’s worth keeping an eye out at used book sales and may also be found at the library.
The Age of Paradise by John Strickland – in form III it is advisable to go slowly with this one and spread it out over the course of a year or more. Makes an excellent world history spine, but parents will want to pre-read or read aloud and edit on the fly when possible because it’s not written specifically for children.