OK. A lot of what you have won't work for that age group like Ping, Sevenpad and most card tricks. Mark Wilson's Book is your best resource.
The first step is to change your thinking from quick, visual magic to longer engaging routines. In a show, you have to draw in the audience's attention and keep it. You don't want to give younger kids the ability to be distracted by providing short, disjointed effects.
I would start out by trying to watch two television shows which I think exerpts are availabe from on YouTube.
The first show is Dora the Explorer. If you compare that to prior children's shows you will see two differences. The first is that the various parts of the show are linked together using the map to provide an outline for a story. Prior shows (like Sesame Street) had disjointed short segments. The overall story in Dora keeps the kids attention longer because of foreshadowing of what is going to happen and review of what has already happened. The second difference in Dora is the interaction. You will notice counting, catch phrases ("Swiper No Swiping"), activities (stand up and waive your arms) and different types of interactions. The theory behind the show is from a book called Theories of Multiple Intelligence by Howard Gardner which talks about the different ways people learn. The importance of this is the idea to work toward a variety of interactons with the kids. You have to go beyond the hackneyed "look don't see" and bumbling magician gags to get the kids screaming. That is one hook (the kids see what the magician doesn't) and one reaction (screaming). Work toward multiple types of interactions.
The second show is called the Upside Down Show. The humor there is absolutely wonderful on multiple levels. It is a great demonstration of how to create characters and a theatrical environment just using scripting and personality. The effect of layering multiple levels provides a really engaging experience -- imagine what the addition of magic would do.
Then, and only then, go and watch videos by David Ginn, David Kaye (aka Silly Billy) and Christopher T. Magician. Finally, go and watch Jeff McBride's Miser's Dream video.
All of that together should give you a lot of ideas about your character and the feel of your show. That really is the starting point for deciding what should be in your show.
The next step is to figure out what goes into the show for effects. My recommendation is to start with some of the classics of magic:
Sponge Balls (you already have) (there is great routine in Mark Wilson's book -- just don't point like he does)
Jumbo Deck $15 (for Mark Wilson's Bigger Card and another card trick like cards across or six card repeat)
20th Century Silks $7.50 or Thumb Tip Blendo $7 (get a Vernet Standard Thumb Tip to use with it)
Wizard Hat Tear $10
25 Feet Magician's Rope $7.50 (for a rope routine in Mark Wilson's book)
Spellbinding Boxes $16.97 (Amazon) (one of my favorite effects)
Breakaway Wand $4.50 (best gag ever)
The key is to come up with interesting and engaging presentations. Then I would add some more classics:
Combo Aluminum Cups and Balls $16.50 with Michael Ammar's Videos or Book
Linking Rings (10 Inch) around $35 (MJM Magic) with the L&L World's Greatest Magic Linking Rings Video
Zombie Ball around $35 (Penguin or MJM) with the L&L World's Greatest Magic Linking Rings Video
Your kids show would have a variety of props and would showcase a variety of different skills (which impresses the parents who are paying the bill). Ultimately, you will want to even upgrade those props to a nicer set of cups (check out Rings and Things), a nicer set of rings (ProLine, Porper or Owens) and Zombie (Morressy or Rings and Things) because having nice props gives a very professional feel.
The other option is to look at the effects put out by Silly Billy and David Ginn and the classic children's effects like Run Rabbit Run, Stratosphere and Hippity Hoppity Rabbits. My sense is that those effects look too much like anyone could do them if they had the props.
