Very tragic. Until the details are out I can't lay the blame completely on Disney yet. The kids were on bikes. I cycle a lot on roads with traffic and there are things you have to do to stay safe when you are biking on a public road.
There are many drivers who are not very good at interacting with cyclists and many cyclists that are not very good at interacting with traffic. I have seen both.
Regardless of the fault it is sad to have people killed anywhere let alone at Disney.