Olson, of 136 Maloy Drive, Winchester, was flown to Washington County Hospital where he was listed in critical condition in the intensive care unit Monday afternoon, a hospital spokeswoman said.
The Michels' grandchildren, Matthew Reyes, 7, and Frederick Reyes, 11, both of Baltimore, were sleeping in the back of the pickup truck at the time of the accident, Shirley said.
When the trucks collided, a camper shell on the back of Michels' truck came off and the two children were thrown from the bed of the truck and into some weeds along the highway, Shirley said.
The children were flown to Children's National Medical Center in Washington where they were both listed in fair condition Monday afternoon, a hospital spokeswoman said.
Virginia Michel was taken to Jefferson Memorial Hospital where she was treated and released, a hospital spokeswoman said.
U.S. 340 was shut down for at least two hours while rescue crews cleaned up the accident scene, Shirley said.
Traffic was heavy on U.S. 340 and W.Va. 9 over the holiday weekend, Shirley said.
In Berkeley County Monday afternoon, state police were expecting a surge in holiday traffic, especially on Interstate 81, as holiday travelers began heading back home from travel destinations, said West Virginia State Police Sgt. M.A. Carte.
As of Monday evening, state police had not reported any serious accidents, Carte said.
Traffic on Interstate 70 through Hagerstown was moderate without any backups or accidents as of early Monday afternoon, said Sgt. K.W. Lewis of Maryland State Police in Hagerstown.
Police expected the traffic flow to increase later in the day, Lewis said.
Staff writer Andrea Rowland contributed to this story.