Two young children are in serious condition following a four-vehicle crash Saturday afternoon on La. 21 at its intersection with La. 40 in St. Tammany Parish.

The children, a 2-year-old boy and a 1-year-old girl, were airlifted to the Interim LSU Public Hospital in New Orleans after suffering serious injuries in the crash, according to Louisiana State Police Troop L.

The children were properly restrained in the back seat of a 2006 Nissan Pathfinder, along with an 8-year-old girl, when a 2012 Volvo 18-wheeler failed to stop and crashed into the back of the Nissan, which was halted behind two other cars in the northbound traffic lane of La. 21, police said.

The cars were waiting for a vehicle to turn left onto La. 40.

The 8-year-old in the back seat of the Nissan, along with the driver and front-seat passenger, 26-year-old Tarrah Willis and 27-year-old Bruce Willis, both of Bogalusa, were transported to St. Tammy Parish Hospital with minor to moderate injuries.

The driver of the 18-wheeler, 61-year-old Earl Johnson, of Meraux, did not suffer any injuries in the crash. Johnson also submitted to an alcohol breath test and passed, troopers said.

Johnson was cited for careless operation of a motor vehicle and having an expired license plate.

All drivers and occupants of the four vehicles were wearing seat belts at the time of the crash.

After the 18-wheeler rear-ended the Nissan, the force of the collision pushed the Nissan into a 2007 Honda CRV sitting in front of it.

The Honda’s driver, 36-year-old Trenice Harry, of Bogalusa, suffered minor injuries and was transported to LSU Medical Center in Bogalusa.

After its initial impact with the Nissan, the 18-wheeler continued north and rear-ended a 2009 Hyundai Santa Fe, police said.

The Hyundai’s driver, 32-year-old Kylandis Jackson, of Bogalusa, was not injured in the crash.