Mary Flora Bell -- England
This eleven-year-old girl caused a sensation in 1968 when she
killed two small boys in Newcastle-upon-Tyne.
http://www.crimelibrary.com/classics/bell/3.htm
http://www.crimelibrary.com/criminology/kidkill/
Book: "Cries Unheard"
(Barnes and Noble)
http://news.bbc.co.uk/hi/english/uk/england/newsid_1935000/1935076.stm