Katherine Heigl reveals how she talks to her adopted daughters about their birth parents

Katherine Heigl said she's been having serious conversations with her adopted daughters about their biological parents.

Speaking in the April issue of Parents magazine, the "Firefly Lane" star opened up about spending lockdown with her three kids: Naleigh, 12, Adalaide, 8, and 4-year-old Joshua.

"This is the longest period I have consistently spent with my children," she explained with a laugh. "At first, I loved cooking inspired meals, but now I'm like, 'Kids, just make yourself a sandwich.'"

Heigl said both Naleigh, who was adopted from South Korea when she was 9 months old, and Adalaide, whom she and her husband adopted at birth in the U.S., have become curious about their birth parents -- and their search for answers has sparked several important discussions.

"We have said to them, 'This is your story. We don't have any information about your biological fathers, but we do have a bit about your biological mothers,'" recalled Heigl. "If you guys want to talk more about them, you can have as much or as little information as you want. Tell us what you're comfortable with knowing."

The "Grey's Anatomy" alum credits her older sister, Meg, who is Korean, for helping her understand how to carry on such conversations with daughters.

She said she asked her big sister about her experiences with racism as a child, especially when she wasn't accompanied by their parents, and became "very angry" after hearing her Meg's blunt reply.

"I was raised with adoption, looking beyond skin color was the norm for me, and I just believed that love is love -- it doesn't matter what we look like," Heigl explained. "But then when I asked my sister, Meg, if she had been treated one way when she was out in public with our parents and a different way when she was out by herself without them, she said, 'Oh yeah, all the time!'"

She said she realized she "had been so naive."

"I had to calm down and realize, 'OK, this isn't about how it makes me feel. It's about how I need to protect my daughters and prepare them for the world,'" the actress told the outlet. "Because I can't change society in one fell swoop."