I think cards could be fine for 9 year olds...though I don't do any card routines in my kids show.

However, I do have a card trick gag in my show.

Picture this:
You ask your kid audience, "Hey, do you guys like card tricks?". They're going to say or yell "yes" even though this is not the best trick to perform for them. That's when you say, "Oh bummer. I don't do card tricks".
You proceed to tell them why by saying that you used to do all this fancy stuff with cards that you can't do any more. While your saying this, you've pulled out a deck of cards and you're dropping them from one hand to the other without dropping the cards on the floor. At the same time, you're explaining that you used to be able to do this but can't any more. Well of course you're doing it and the kids will eventually say, "You're doing it". I believe this is based off of something I saw in a David Ginn book. Once the kids tell you that you're doing it, you then suprisingly realize it and get excited to the point where you reveal that the cards are all connected. Then I like to throw in a gag that the kids might not get, but the parents will. I say, "you know that big red button they show on TV? You know? The EASY BUTTON?" As they're shaking their heads yes, I hold the cards apart and simply say "STAPLES". No magic, but a great gag filler.

Additional quick gag-line: If you use the larger printed cards that have about 4 WILD cards, arrange it so that they together, somewhere in the middle. Before you do your "STAPLES" gag-line, locate the WILD cards and hold the connected cards up so that these are clearly exposed. Then say "Hmm! That's Wild!"

Again, it's not really magic...but it's fun and funny.

Hope you like it.

^ I surely liked it. Sounds like it would get a laugh out of the adults.