A 5-year-old girl was slashed in the face by a teenager who was horsing around with a knife on a Bronx sidewalk Friday afternoon, cops and law enforcement sources said. 

The girl was walking with her mother on Third Avenue – near Walter Gladwin Park — around 3:10 p.m. when they passed a group of teens messing around at the corner of East Tremont Avenue, the sources said. 

During the horseplay, one teen accidentally dropped a knife on the ground.

As he picked up the knife, he somehow slashed the young girl on the side of the face, sources said.

It’s not clear whether the slashing was accidental or not.

The youngster was taken to St. Barnabas Hospital, where she was listed in stable condition.

The teens — who are strangers to the girl and her mom — fled east on East Tremont Avenue.

No arrests were immediately made.