"They made a beautiful lunch for me and at one point I said, 'Is that a bullet hole in the mirror?' Chastain said.
"And then I looked at the ceiling and there were bullet holes, and then I looked in the chair I was sitting [and it] had bullet holes, and there were little kids … like a 6-year-old and a 4-year-old, and I just don't understand what is happening to the world."
Chastain said she felt a responsibility to use her celebrity to shine a spotlight on those who needed it.
“I understood how sad it would be … when I was meeting the kids at the hospital, I felt, just my heart was going out to them, because there was a girl with her mom and she needed new legs, right?
"So that was really devastating."
Chastain also visited Okhmatdyt Children's Hospital, Ukraine's national news agency reported.
The actress joined the growing list of A-listers who have visited Ukraine in a show of support for the country after Russia's invasion.
Mr Zelenskyy has met actors Sean Penn, Ben Stiller and Leiv Schreiber, and actress Angelina Jolie visited Lviv to meet people displaced by the war.