In Elgin Independent School District v. R.N., 191 S.W.3d 263 (Tex.App.--Austin 2006, no pet.), a five-year-old child was left asleep on a school bus and the bus was locked.
The child remained on the bus for several hours.
The Austin Court of Appeals held that while the bus driver's failure to unload the child was a failure of supervision rather than a "use or operation" of the bus, the driver's action in locking the door constituted a use of the vehicle. Id. at 272.