Vin Diesel stepped in to take care of 4 kids when their father -- one of Vin's longtime friends -- got busted for a domestic violence incident with his girlfriend.
Law enforcement tells TMZ ... Vin's pal, Valentino Morales, was arrested last week after allegedly pushing his girlfriend and hitting her in the face. Morales says his daughter immediately called Uncle Vin for help. We're told he stayed with the kids while Morales was taken into custody.
Morales was released and his girlfriend decided she would not press charges.
We're told Vin is the godfather of Morales' kids, and did a great job calming them down during the incident. See, "The Pacifier" actually was good for something.