Sorry about the damage to your car. I remember my first car. I was very protective of it, but occasionally things would mysteriously happen to it in the school parking lot. Things like this usually happen for one of two reasons (or both): jealousy or lack of respect for other's property.
The unfortunate thing is that there is little you can do about either of these things. I wouldn't suggest keeping this a secret from your parents. It wasn't your fault, so there is no problem there. They may also be able to help you out in a situation like this, even if it's only advice on where to take it for repairs.
2008 BMW 535i Space Gray, Black Leather, Dark Bamboo Trim| Sport Automatic with Paddles | Sport Package
2008 BMW M5 (gone, but not forgotten) Space Gray, Silverstone Merino Leather, Madeira Walnut Wood Trim | 7speed SMG | All options
Mods: Corsa Exhaust | RPI Ram Air Intake | H&R Sport Springs | Rogue Engineering 12mm spacers