Full Disclosure: The handheld gaming devices and accessories were gifts from the grandparents both sets. In other words, my parents and 6/10ths parents went together to buy them.The game players are definitely the top gifts of the year. They even discovered the wireless IM feature and used it when they were supposed to be sleeping last night.
That wireless capability is actually kind of cool. You can buy one copy of Mario Kart and when one starts the game he chooses multiplayer/simple and then the other kid can connect wirelessly to the game. It transmits the game through the "ether" and then they race each other.
At first, 1 of 2 won every time. But 2 of 2 started to get the hang of steering and also enjoyed doing goofy things, like driving off of bridges into the water. By being silly he discovered some "shortcuts" and started winning consistently. 1 of 2 was convinced that the computer was driving for him because "no one can steer that smooth!" I had them switch consoles and race. 2 of 2 still won, even though 1 of 2 now had the computer assisted car. That just made him madder. We told him that he needed to figure out why 2 was winning and copy his techniques. By the end of the evening, 1 was more competitive.
Another case of fratricide avoided.