Kimora Lee Simmons Says She Co-Parents 5 Kids with 'Me, Myself and I': 'I Do the Heavy Lifting'

Kimora Lee Simmons has every reason to smile.

Speaking with PEOPLE about her work with Smile Train on World Smile Day, the model and entrepreneur talked about how the organization's work supporting cleft surgeries for children worldwide compelled her to become an ambassador.

"In my daily life, I'm a mom of five. Our children's happiness, something as simple as seeing them smile, makes a huge difference to us. On World Smile Day, we want to always remind each other to smile."

What makes Kimora, 47, smile is quality time spent with her children — sons Wolfe, 7, Kenzo and Gary, 13, and daughters Aoki, 20, and Ming, 22.

"My kids, our kids' happiness is really what moves me and moves every mom, every dad, every parent, every caregiver," she shares. "Seeing smiles, on my kids' faces is to see your kids smile."

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Kimora has also learned to smile at herself and the work she does to keep her family happy.

"It's usually me by myself with my kid five kids, right? And so in that sense, I do most of the heavy lifting. I do it all. It's not co-[parenting]. It's a trio — me, myself and I."

Kimora shares daughters Aoki and Ming with ex Russell Simmons, son Kenzo with ex Djimon Hounsou, and son Wolfe with Tim Leissner.

Though her daughters live on the East Coast — where they're each finishing up their respective college degrees — and she's in Los Angeles with her sons, the two young women come home often and are close with their younger brothers.

"They're so funny. They make me laugh," the proud mom says. "Just to see them all healthy and happy and driving or in school and living life. I'm happy for them. You want them to win, so I'm happy and I'm proud."

Noting it's the "everyday moments with my kids" that she loves, Kimora shared that her boys are very "outdoorsy" and are "very much get-outside-and-do-things kind of kids."

In part, that may have to do with Kimora's rules around screens, which she suspects are "stricter than the average household."

"You don't just have a phone and an iPad off in your room. If you need to go on a computer or you need to use a phone, it's in a kind of public area of the home," she explains. "Of course, you can use it, but it's more like being in a library, versus being in your room on the phone."

Acknowledging that the way she does things is a "little bit different," she says the policy worked with her older kids.

"That's something that I did with Ming and Aoki as well. Of course, as they get older, everybody makes their own case for balance and whatever, but we're not there yet."

Asked to give a word of advice to other parents looking to raise happy kids who spread joy, Kimora said that "it's important to be there and to show up."

"Everybody is trying to do their best," she notes. "I think it's important to talk to your kids and to make sure they feel that you are present, that you're there, and that you love them."

"You may not always see eye to eye — or maybe you do see eye to eye — but just showing up and being there is a big part of it."

Kimora adds, "Be forgiving of yourself. You don't have to be perfect, but be present."