Douglas Kennedy was “calm” and “collegial” with two maternity ward nurses who tried to stop him from leaving a Westchester hospital with his newborn son, a friend testified yesterday.

Kennedy, 42, the youngest son of assassinated New York Sen. Robert F. Kennedy, was not the aggressor in an incident that resulted in his arrest on harassment and child endangerment charges, said Kennedy’s buddy, Timothy Haydock, a doctor at the hospital.

Haydock, an emergency-room physician at Northern Westchester Hospital in Mount Kisco, said he was with Kennedy when an “aggressive” nurse lunged at the father as he backed into a corridor stairwell.

“He didn’t raise his voice. The real aggressive action came when the nurse lunged at Douglas and tried to grab his baby in the stairwell,” Haydock said,

The infant was unharmed, Haydock added.

Nurse Cari Luciano claims Kennedy kicked her, and fellow nurse Anna Lane said he twisted her arm when they tried to stop him from leaving with the 2-day-old boy Jan. 7.

Kennedy, a father of five, was arrested weeks later.