It's hard to see small animals in vehicles in general. The problem was caused more due to the fact that the dog ran into the road, and not because somebody wasn't paying attention.
I'm assuming the driver of the van was probably going between 25-45 MPH. Even if he did the the dog, he probably wouldn't have been able to stop fast enough to not hit the dog. That and if he tried to swerve out of the way of the dog, he could have either hit your family or another car.
It really sucks that your dog got hit by a car, but it's not necessarily the driver's fault.