Oprah Reveals Her 'Greatest, Deepest Joy' in Life, and It Will Make You Want to Give Back

While Oprah has not had any children of her own, there are a handful of girls out there that are like daughters to her -- and they’ve filled her with a great deal of joy and purpose.

They are the students and alumnae of the Oprah Winfrey Leadership Academy for Girls in South Africa, and to them, she is simply "Mom O."

That leadership academy has had some incredible results: The boarding school has seen 90 percent of graduates enrolled in colleges including Harvard and Oxford.

“They are my greatest, deepest joy,” says Winfrey. “I wanted to build a school for girls who are like me,” Winfrey told PEOPLE.

Winfrey, who grew up struggling, knows how poverty can impact every area of a girl’s life. She says her girls “have been in the heart and heat of poverty. Poverty itself is a traumatic event, just trying to be able to have food on your table every day. Most girls have lost one or another really close relative, sometimes both mother and father.”

But of course Oprah is aware that she is not actually these girls' mom, and wants to make sure they are aware as well. “When the girls started calling me Mom O, I did not want their mothers or their legal guardians to think that I was stepping in and trying to take over the role their mom mom holds in their lives,” she says. “I’m very much aware of who I am and what my role is for them.”

I like babies, but I like them like, ‘Hi baby, okay, now go over there.’ I like children when they can actually speak to me and tell what is the problem. This is how having children was supposed to manifest for me.

“They’re the daughters I did not have,” Winfrey, who’s turning 65 on Jan. 29, says. “I never thought that that mothering instinct was something for me. I like babies, but I like them like, ‘Hi baby, okay, now go over there.’ I like children when they can actually speak to me and tell what is the problem. This is how having children was supposed to manifest for me.”

It looks like those girls and Oprah are making a big difference in each other's lives, and they are all richer for it.