You could develop a whole course from Mark Wilson's Complete Course with some additions from Scarne on Card Tricks and Hugard's Encyclopedia of Card Tricks. Also, the Fulves "Self Working" books have a lot of material. You can teach card tricks to kids who are six or older. You just have to keep the effects appropriate to their age. But you need to do more than just card effects.
A lot depends on how old the children are and how long the class is going to be. That is, there is a difference for teaching 5 year olds for a half hour (where you would teach a couple of tricks, but it should include a lot of performance on your part) and teaching 9 year olds for an hour a day for week (where there would be more structure, practice and performance by the children).
One of the biggest stumbling blocks for young performers is actually performing. Especially with the more complicated routines that require a lot of interaction with the spectators. So, there should be a lot of performing. If it is a week long, you might want to think of having a show for the parents at the end of the week where the kids can perform what they have learned (and video taping it so the kids can get a copy).
You also might want to think about assembling a magic kit for the kids. It might include two decks of cards (one red, one blue -- bridge size if they are under 10), a children's TT, some silks, gimmick tricks (drawer box, ball vase, etc.) if the kids are younger, some rope, sponge balls and maybe one effect that is different for each child (like Silk Blendo, Sponge Ball Blendo, rising card, Hovercard, etc.) which they can use as part of their performance. If the kids are 10 or older, you might want to include a selection of basic gaff cards (double back, double face, blank back, blank face, short card) and stripper deck, a one-way deck, an invisible deck or a Svengali deck.
I've got lots of ideas and would be glad to discuss futher.
