Not sure exactly what the parameters are for what you need (ie are you teaching a specific language?), but as far as making it appealing what about using Gamemaker? The kids would be creating games, so it's not just about boring coding for the sake of coding (has anyone ever really wanted to say hello to the world??) but for the sake of accomplishing a goal, which is what coding is about in the real world.
You can start with the beginner's interface using mostly drag and drop commands, to teach logic and problem solving without getting bogged down in syntax. Then you can switch to the Advanced interface and let them code their own stuff (this can actually also be done within the Beginner's interface as well).
Game making does appeal to both boys and girls, obviously not to every boy and girl but neither does coding. You're never going to appeal to everyone anyway.
I've only done this once so far and it was a very small group, but the interest rate was VERY high (it was mixed though, both boys and girls).