Nintendo DSi question.?

i just bought a game called "Fireman Sam" from europe...cost me around 11 us dollars....but it wont work with my sons Nintendo DSi....why is this???? the game is legit...it was wrapped up and enclosed like the games from our stores....but for some reason my DSi doest not read it...what should i do so my son can play this game...i checked...this game isnt sold in the US..only in europe...