A grandfather was busted for stabbing an ACS translator who suggested that his grandkids were dirty at their Brooklyn home, according to a source and police officials.

Quanyi Feng, 61, was interviewing with the translator, a 55-year-old woman, at the home on 52nd Street near Fifth Avenue in Sunset Park around 8 p.m. Thursday, cops said.

The Cantonese translator, along with an ACS worker, visited the home — where Feng lived with his 7 and 8 year old grandkids, after receiving an anonymous tip about the 8-year-old’s poor hygiene, a source said.

The family became upset — and as the workers got ready to leave, Feng allegedly pulled out a knife and plunged it into the translator’s back and lower torso.

She was taken to NYU Langone Hospital-Brooklyn with non-life-threatening injuries, but needed to undergo surgery, the source said.

It wasn’t immediately clear if the family had any history with ACS.