I'm so sorry, the family has my prayers. I lost a schoolmate every year from 8th grade until just after graduation. It's so hard when they are so young.
My niece was killed in a car wreck at the age of 15. It is a horrible thing for any family to have to experience. I remember talking with my sister and her telling me how much receiving cards meant to her. She was able to read a card, know that person truely cared, react in private and not have to respond.
So maybe you could take a moment and send the family a card, to let them know you care.