Playing Wii is fun...and good for you!
Although video games should never replace real sports, occasionally playing these active video games can be good for you. However, keep in mind that not all active video games are the same: energy expenditure during Wii boxing was 50% greater than during Wii bowling.
Here's an inexpensive way to get the Wii. The Wii Mini Console System comes with the Mario Kart game and is only about $125! Compare that to the non-mini Wii and you'll save several hundreds of dollars. The difference? The mini Wii does not connect to the internet or have a USB or SD slot for viewing your pictures. It will play any Wii game, and you can hook up the basic Wii remote, the nunchuck, or even the steering wheel. If you want to use the balance board package (below), you will need to have a console.
The Wii Fit software and Balance Board bundle sells for only about $120, which can be used with any existing Wii system (except the Wii U). It includes the game disk with tons of workout routines, including both yoga and strength training. You can improve your balance, target certain body areas like your abs or glutes, and get a range of fun workouts that will increase your heart rate and help you and your kid stay healthy and burn calories. The balance board is wireless and runs on two AA batteries.
Graf, D.L., Pratt, L.V., Hester, C.N., & Short, K.R. (2009). Playing active video games increases energy expenditure in children. Pediatrics, 124, 534-540.