The attack happened Friday night about 10 miles northwest of Aspen, Colorado, according to the Pitkin County Sheriff's Office.
A man called 911 dispatchers to report that his son had been attacked by a mountain lion and he was driving to the Aspen Valley Hospital, police said in a statement.
The boy's mother told police that the boy was playing outside with his older brother when she heard screams. The mother ran out and "physically removed her son from the mountain lion," according to the statement.
After initial treatment in Aspen, the boy was transferred to Children's Hospital in Denver. He's in fair condition with injuries to his face, head and neck. His mother was treated and released for minor injuries to her hand and legs.
The family has not been identified.
After the attack, deputies and an officer with the U.S. Forest Service located a mountain lion in the area and the animal was put down, police said.
Investigators are also looking into reports of a second mountain lion in the area earlier in the day.
Though mountain lions are not uncommon in Colorado, sightings are rare.
The Colorado Parks and Wildlife website
gives residents tips on what do if encountering a mountain lion, including fighting back if attacked.
"People have fought back with rocks, sticks, caps or jackets, garden tools and their bare hands successfully," the website says.
"Lion attacks on people are rare, with fewer than a dozen fatalities in North America in more than 100 years," Colorado Parks and Wildlife said.
Mountain lions are also known as pumas, cougars and panthers.