From PEOPLE Magazine Click to enlarge
For months Brooke Shields has been juggling the demands of her career and raising her two daughters with another difficult task: caring for her mother, Teri, 75, who—as Shields recently revealed—has been diagnosed with dementia. Her relationship with her mother (who managed Brooke when she was a child star) was always a challenge, and this new chapter "takes a lot to get used to," says the actress, 44. As she began a new job as spokeswoman for Coppertone's NutraShield beauty line, Shields spoke to PEOPLE's Alexis Chiu about her struggles as a daughter—and joys as a mom.

How are you holding up?

It's always difficult when you see your parents incapacitated. My father [Frank, a Revlon executive] died of cancer. You fight it at first and then try to realize that the roles have to change. It's just never easy, especially when you're in this "sandwich generation" where we're taking care of our parents and we're taking care of our kids too.

How's Teri doing?

She's good. It's all been a whirlwind; she doesn't quite understand. But she has a good team [of caregivers] around her, which is good.

How did you explain what's going on to your daughters [Rowan, 6, and Grier, 3, whose dad is Shields' husband, Chris Henchy]?

You have to talk to them and make sure they don't feel threatened. They don't understand when someone can't follow what they're saying or gets impatient with them. I'll say to [Rowan], "You know when your sister bugs you or wants to have your cake or pull your hair? It's the same thing." You just have to know what you love about someone.

How do you feel now watching your kids grow up?

I tell my little one, "If you want to be a big girl, fine. But you know you're always going to be my baby." You think you'll always be your parents' baby, and when the roles change, it takes a lot to get used to it. You have to start looking to yourself. I'm the child of an alcoholic—so doing that seems to be, unfortunately, par for the course. And I'm an only child. It all has always fallen on my shoulders.

You brought the whole family together for Mother's Day.

It was really sweet. We had brunch in New York—my family, my mom, some friends. One [daughter] gave me a lavender plant, the other one gave me a sunflower plant—my two favorites.

Hard to imagine one day they'll be grown-ups?

I look at them and think, "God, I hope they're gonna join forces and take care of me when I'm old." You hope that you've earned it—that in a way, you've earned their respect.