Yes, it's a kids' book, and it's only about fifty pages long, so there's not much to review.  It's still worth a look.
 
 

There are five chapters, each divided into subsections.  Each of these sections briefly covers some historical happening or issue.

Chapter one introduces the murder, then covers the layout of the cathedral grounds, the knights, and a fuller account of the murder according to Edward Grim.

Chapter two covers Thomas's childhood, London in the twelfth century, what schools were like, and Archbishops Lanfranc and Theobald.

Chapter three includes a little about Henry, the state of England after Stephen's reign and the need to restore order, the Angevin empire, and what various royal ministers did.

Chapter four: Thomas as archbishop, the rights of the Church, the constitutions of Clarendon and the quarrel, exile and return.

Chapter five: Thomas as a saint.  Miracles, pilgrims, and Henry's penance.  The "end of the quarrel" under Henry VIII.

As I said above, it's a children's book, but it's still useful in certain ways, even for adults.  It provides a quick overview of the whole story, even if it is a sort of G-rated view.  It also explains things that other books assume you know, like what exactly a chancellor does.  The many illustrations are particularly useful.  There are pictures from medieval manuscripts, plans of the cathedral grounds and of London, photos of castles and cathedrals, and artists' renderings of particular scenes and people.  For example, there's a drawing of FitzUrse that's used to illustrate the equipment of a knight of the period.

My one gripe is that the book depicts Thomas as wearing full archiepiscopal regalia on the day of his death (as if he'd had time to dress properly when he was hustled out of his house toward the cathedral).  But the remark about Anouilh's Becket partly makes up for this: "[the play] returned to the story of two quarrelling personalities and got most of the facts completely wrong" (p 48).