Something definitely smells out of place here. I believe the AdWords policies vary from country to country (and from time to time) but the last I checked (2015), here in India, you had to have at least one verifiable payment method (card/bank account) in order to even activate an AdWords account, leave alone the matter of running up a balance of Euro 100,000. So how did a 12 y-o manage to do that?
In this case, if you pay for AdWords credit up front and then spend them, the company is fine. But if they charge a bill after the fact, the contract allowing those charges wouldn't be legal, and that's the responsibility of the professional part.