(From my experience) Young kids don't fully understand some aspects of the cups & balls. Having said that, you still get a good reaction with the surprise ending. But for the most part they don't understand!

If you have a fairly easy to understand routine and something they can follow it should go down ok. Another idea is to add a story to your routine, this would make it more interesting and easier to follow.

Carl Andrews - Table hopping cups & balls.
In this DVD Carl teaches his Cups & Balls and sponge ball routine. I don't think either of these routines are suitable for kids and therefore don't recommend this DVD. (the routines are for adults) What you learn is a routine, not the principal of the cups and balls.

(Example: If I want to play the piano should I learn a tune or should I learn the keys? If I learn a tune I will be able to play that one tune, but if I learn the keys I will be able to play many tunes).

Do you see what I mean? The same goes for magic, if you learn the fundamentals you can do many routines (even create your own) if you learn a routine you can do just that one routine.

If you want to perform cups & balls get something like: Michael Ammar - Cups & Balls. This will go through most of the fundamentals and a few routines!

Wow man, you should give yourself more time. Don't just get a bunch of gimmicks. If you do this then there will be no routine. It'll just be "Hey here is a pen through a dollar" , "Look! The pictures in this coloring book are colored now", "Check this out, I can make a dollar bill float"

My advice would be to find tricks similar to eachother. I have no experience with kids shows, but I have performed for family. Figure out a way to glide into the next trick.

For example, you could do the basic cups and balls trick, and at the end have sponge balls come out of the cups. Then you make 3 sponge balls turn into 1 giant one in a kids hand. And then make the sponge ball float.

I just made that up, I'm not sure what kids that age enjoy, but just try to include them in the trick. I know they love that because of my 5 year old nephew!

Hope that helps.