to think the wii fit shouldnt say

[biddysmama]

"at risk of becoming overweight" to my 9 year old

he keeps telling me that he's going to be overweigh, the wii fit says so even tho he is the 'correct' weight for his height... bought the bloody wii fit so he could play something without just sitting on his arse

Don't weigh him on it then. BMI charts aren't really suitable for children and I believe it does say that somewhere in the info.

why is a child on the wii fit. give him a real game

I believe the bloody Wii was one of the factors that exacerbated my niece's eating disorder.

The wii fit is great if you use it properly. I love mine, it has been very helpful in losing weight and becoming fitter. My kids like to use it as well.
As far as the BMI charts go they don't really apply under the age of 12. I weigh my daughter [age 11] on it now and again just out of interest although I can clearly see she is in her normal health range. If she was 'in danger' of becoming overweight ie borderline, I would rather know.