The man, who was not identified, was detained this afternoon at the San Bernardino County Sheriff's Department's Adelanto station, spokeswoman Cindy Bachman told the Weekly.
It's not clear what crimes are being investigated:
The video titled "my nephew messed him up for picking on his home boy" came to the attention of San Bernardino authorities after KTLA News made them aware of it last night, Bachman said.
Cops started looking into these facets and allegations, she added:
-An adult is videotaping the fight.
-Another adult is seen ensuring that boys watching don't "interfere."
-The video was posted to the Facebook account of someone identified in reports as Austin Gamboa.
There were two small children fighting for at least a couple minutes, and one adult male was somewhat encouraging them and also kind of keeping the other very young spectators from interfering with the fight.
It's not clear if either of the fighters was injured.
KTLA and CBS Los Angeles say the fight took place in Victorville.