Malala: Activist for Girls' Education by Raphaele Frier
If you select only one book about Malala for young readers, make it this one. This is a clear, straightforward presentation of facts. It is not so harsh as to become disturbing (no grim details) but does not soften reality (the narration states very plainly that Malala was shot, with bullets striking her head and neck). Young readers will learn a lot from the main text and much more from the afterward which has loads of cultural and historical information as well as resources for learning even more. With eye-catching illustrations as well, it's an all around win.
More information: Malala: Activist for Girls' Education releases February 7.