Obviously little is known for sure, except that it looks like a terrible tragedy involving a large number of children. Condolences to all affected. Three quick points.
1) The airplane in question, a Pilatus PC12, is a well-known, reliable, admired, sturdy craft. I have a friend who flew his family all around the world in one. I have flown several times in his airplane and once in another PC12. Picture below of a PC12 is from a European site; a picture of the airplane that reportedly crashed, N128CM, is on FlightAware.com, here.
2) The PC12 is a big, comfortable, spacious airplane. But if there really were 17 people aboard, that would be a lot. Cutaway view of interior in "executive configuration," from West Branch Air services, below. I believe that in other configurations it can be certified for a total of 12, two pilots and 10 passengers. Even if passengers are small and light, so total weight is not an issue, certification limits usually depend on the number of separate seats and seat belts available:
3) I have landed at all the airports involved in this flight -- Vacaville, Oroville, Bozeman, and Butte -- but particularly noted the flight's origin at the beginning of the day: Redlands, California (my home town). If it really was a plane full of kids on a skiing trip, this will be a community-wide disaster for some small California community. We don't know which one yet. Sympathies to whoever the grieving town and families turn out to be.
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