Naomi Watts has admitted she "cried" sending her son Sasha off to college.

The King Kong actress opened up in detail about letting her children grow up and move out, sharing a heartfelt social-media post about a weekend spent delivering son Sasha to his new university dorm room.

"We packed and unpacked, stacked and color coded. We walked and walked, woke up early with excitement," Naomi, 56, wrote in a caption accompanying a series of snapshots of herself in the process of helping Sasha, 18, settle into his dorm room at the University of Southern California's School of Dramatic Arts.

She admitted the experience hadn't only brought out their best sides.

"Then we shopped and shopped, and sometimes fought about stupid stuff," Naomi continued. "We laughed, we cried, I had a few extra secret cries and maybe some not so private ones. We hugged a lot. We built things, we talked to robots, we ate good food. We got lost a bunch."

Naomi reunited with her ex-partner Liev Schreiber - Sasha's father - for the trip and shared some reflections of his own to Instagram.

"Starting to feel the pull," Liev, 57, wrote. "Gonna miss my ride or die. Having said that, USC is gonna get one of the deepest, kindest, bravest and most beautiful boys I have ever known."