Out of control bus, and driver

I pick my grandson up from his bus stop in the afternoon, now mind you he is only seven years old, and in first grade. The filthy language that comes out of these kids mouth that are on the bus and the ones who get off at his stop is totally out of control. Not to mention the bus driver her self. My grandson gets off the bus and tells me that the bus driver was saying bad things. I ask him what she said and he said PaPa I’m not allowed to say that. I told him I needed to know what she said; so he told me. This is the quote from a seven year old boy, “if you kids don’t sit down and shut the F**k up I’m turning this bus around and taking you back to school.” What’s up with that, and on top of that there is a ten year old hitting and teasing my grandson and the driver does absolutely nothing about it.

I have to do something about what is going on, so I am asking for advice on the best course of action on the matter, as far as who would be best to contact. The principle, The buses supervisor, or that parent.