Headlights wont turn OFF - 2004 325i

Help, just got a call from my son (17yr old Jr in High School) that the headlights on his car wont turn off. This car is new to him (had about a month), the grandparents bought it for him. I havent a clue. Someone suggested disconnecting the battery until we can find an answer or get it to be looked at but husband says (who is out of town today) we could short out the electrical system. Again, I am clueless!!