I just bought Kinect Kinectimals and I took the same time to play with my little nephews. If indeed, the game can quickly seem boring for an adult, he truly has a hypnotic power over the young. However, they tend to get too close to the screen to "touch" the tiger, but other than that, they are fascinated by this game, and I find the concept (which reminds me EyePet on PS3) is very successful.
A great gift for Christmas (although a bit expensive if you do not already have Kinect)