UPDATE: 8/24

Law enforcement and bear management staff investigated the incident and determined that an adult female grizzly bear injured the 10-year-old boy from Washington.
Tracks observed by staff indicated the grizzly bear was with at least one cub-of-the-year or yearling bear.
The bears were likely foraging next to the trail when the encounter occurred.
Park rangers do not intend to search for the bear since this incident was a surprise encounter with a female grizzly bear defending its cub.
“This incident could have been more serious. We applaud the family for traveling in a group, carrying bear spray, and knowing how to effectively use it during their emergency,” said Yellowstone National Park Deputy Superintendent Pat Kenney. “We wish their son a full recovery from his injuries.”
The Divide and Spring Creek trails remain temporarily closed. They will reopen after the trails have been inspected for recent bear activity.

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Original post: 8/23

Around 10 a.m. Thursday, August 23, a family of four from Washington encountered a bear a half mile up the Divide Trail, southeast of Old Faithful. The son, 10-years-old, ran away from the bear when it charged out of vegetation towards the family.
The bear chased the boy and knocked him to the ground. The parents effectively deployed bear spray about five feet from the bear’s face. Thereafter, the bear shook its head and left the area.
After the incident, the family walked back to the trailhead, drove to the Old Faithful Ranger Station, and were directed to the nearby clinic. The 10-year-old suffered an injured wrist, puncture wounds to the back and wounds around the buttocks. He was transferred to the Big Sky Medical Center.
Law enforcement and bear management staff responded immediately to the area and are currently investigating the incident, including looking for signs that would identify the bear species. The Spring Creek and Divide trails are temporarily closed.

Yellowstone National Park contributed to this story.