You have to write whichever book it is that wants to be written. And then, if it's going to be too difficult for grown-ups, you write it for children.
Right on, sister. The other thing I wanted to tell you is to GO SEE PERSEPOLIS. The movie adaptation is fantastic and covers both the original graphic novel by Marjane Satrapi and its sequel. For more info, check out this excellent documentary clip (courtesy of TadMack).