Also, I'm collecting NINJA party ideas on pinterest... link here!
Start with Ninja, Cowboy, Bear (Bruins and Leung) and learn about Ninja strengths through comparison to others. Wonderful storyline that shows how three friends had trouble getting along but worked it out (for siblings, too!). Has a fun "game" at the end akin to rock/paper/scissors that you do with your whole body... maybe I'll have to capitalize on this active game at the party. We'll be reading this one again! The story appears to be one in a series of three. Sure wish our library had more!
Not really a Ninja story, but still fun to read and with cute illustrations, The Boy Who Cried Ninja, by Alex Latimer is pure imagination! Mysterious creatures show up and wreak havoc, but who would believe in those creatures... unless you invite them to a party! The nonsense appeals to my sleepy, exhausted boys at bed time. They can relate to the boys' relationship with his parents, ie. they won't quite believe him and he keeps having to rake leaves! :)
Wink, the Ninja Who Wanted to be Noticed, by J.C. Phillips is a darling tale that inspires individualism. Sure SILENCE and stealth are the weapons of the ninja, but Wink just wanted to be noticed! Is there anyway the two can meet? At the circus! Even the master acknowledges the great fit.
In Wink, the Ninja Who Wanted to Take a Nap, by J.C. Phillips, the famous Ninja is tired after performing as the star in the Lucky Dragon Circus. He can't escape his fans though, who keep him awake! His master gives him wisdom, but he doesn't understand it... then he sees it, and finally figures out a way to get his rest.
Ah, Mary Pope Osborne! Magic Tree House stories are a perennial favorite, and here is one (Night of the Ninjas) perfectly suited to our quest of learning about Ninjas...