Is Flying Safe With Femur Fracture?

On Saturday my 22 month old grandson broke his femur (spiral fracture) while visiting us in Florida. He is in a spica cast and we are trying to find out if it is safe to fly home tomorrow. The surgeon we took him to is not returning our calls about this and m son & his family must leave soon. Is flying safe with such a new fracture or should they take a train?
Margaret