I bought a Kinect last week then injured my shoulder the next day (not related to the Kinect purchase). That means I have not had a chance to test it. The Kinect adventure and Kinect sports have been getting mid rate reviews. Keep in mind the reviews have already seen ping pong and soccer on the Wii. I find the games to be more challenging. You need to swing at the right time and in the right place instead of just flicking the Wii-mote at the right time.
The dance game has been getting good reviews because it his truly a full body game. You can play the demo on the Kinect Adventure there is bonus content on the lower left side of the title screen.
When your daughter is not around you should try the demos and see if you want her dancing the way the game shows.
I suggest you set up the Kinect (figure out where you are going to place the sensor and where you are going to need move the couch) the set up takes about 5 minutes and you need the room to be quite while the audio configures. Take the time to use the supplied calibration card to fine tune the sensor.
Then put the Kinect back in the box and let her open it on Christmas. When you plug the Kinect in the back of the Xbox it will recognize the sensor and realize it has already been set up and you are good to go.
Send me a pm if you need help setting it up, I am a big enough geek to help over the phone.