Look at the Alfred Publishing "First Year Charts" and "Jazz Beginning Series".

I start up my jazz band before the winter concert.
Look at The Herald Angel Swing and Doctor No-el. They work up quick and kids love them.

Fall or spring look at charts like Ants in the Pants and Burritos to Go. There are many others too that are great for a young jazz band.

I also like that they include parts for other non traditional jazz instrumentations. I personally let everyone join jazz band at the middle school level no matter what instrument they play.