Police have questioned a teenager they believe is behind a twisted viral video that shows two young grade- school girls forced to fight one another in The Bronx.

Cops said the 17-year-old sister of one battler helped orchestrate the cruel brawl, which was posted on YouTube this week.

The video shows 6- and 7-year-old girls in puffy winter coats pulling each other’s hair and slapping one another at Poe Park in the Bedford Park section.

Police said they spoke to the mother of one of the young girls, and have questioned the 17-year-old about the incident.

Throughout the video, a female thug behind the camera can be heard egging on the terrified girls and shouting out the name of a viral-video Web site.

Cops said others may be involved.