Deputies from the Fort Bend County Precinct 4 Constable's office responded to reports of an accident on the Fort Bend Tollway at FM 2234 around 6 p.m.
Constable Trevor Nehls said the vehicle with the two children inside was following a relative who had a flat tire when a large truck struck the rear end of their vehicle.
Five people were transported to the hospital, the two children were transported by Life Flight in critical condition.
There's no word on the kids ages, but deputies said there were no child seats inside of the vehicle.