The accident happened just before 6pm on Interstate 45 between Wilson Road and Texas 105.
According to Conroe police, a Dodge Dakota hauling a bass boat was southbound. Officials said the driver -- identified as Melton Brown, 64, of Spring -- lost control when the boat trailer started jumping, possibly due to a tire issue.
The pickup clipped a Ford Explorer that was traveling next to it, hitting and slicing its tire, police said. As the truck spun with the trailer, the SUV started flipping.
The truck came to rest facing traffic in the southbound lane.
The boy and two grandparents were in the SUV. Investigators said the child, who was asleep in the back seat and not in any type of a safety restraint, was ejected as the SUV came to rest upside-down against the right shoulder barrier.
The boy landed 87 feet away on the exit ramp to Texas 105, officials said.
Police said the child was taken to Conroe Regional Hospital in critical condition with a skull fracture, concussion, broken hip, broken elbow and broken ribs. He may be transfered to Texas Children's Hospital.
The boy's grandparents -- 60-year-old Charles Hughes of Houston and his wife -- were also injured in the crash. At last check, they were both stable.
Brown was charged with intoxication assault and felony driving while intoxicated.
The accident remains under investigation.