For a real gem of a book on Children entertainment, consider David Ficus book on Birthday Magician Handbook. The title is deceiving because it focuses on Birthday Parties, however, the information is transferable to other types of children shows.
Also, Check out the material and books by David Ginn at: David Ginn's Web Site
I have a lot of his work and it is great stuff. Also his videos will help you speed your way to your goal.
Check out Samuel Patrick Smith at: Samuel Patrick Smith's Website
Both have good material. The real key to multiple shows is the comedy bits of business you can add to a routine. A show need not be made up of 12 or so tricks, it can be four tricks, with 50% comedy added t it. Ginn shows you a lot in this area (Kidbiz). Remember we are working with kids, not adults, and you must perform at their level with them, not above or below them.
Performing Magic for Children
by Schenk and Sondermeyer is the only know research text on the subject of entertaining children. Good Children Magicians have know this for years and Schenk confirms it.
Dont ignore Safety Magic for Children
by Karl Wagner, where you can put a fresh routine to your existing tricks wwwith a safety message attached to it.