Peter Mutabazi has fostered or adopted 36 children in the past seven years — by himself.

Right now, he's caring for kids aged two, three, seven, eight, 10, 17 and 19 years old, three of whom are his adopted children.

His is an extraordinary story. Raised in rural Uganda, Mutabazi ran away from home at the age of 10, becoming a street kid in the capital city of Kampala, sleeping under stationary vehicles, selling peanuts at a bus station and surviving off fruit taken from stands at a market.

"I grew up [the] poor of the poorest," Mutabazi told CNBC by video call. "I became a street kid, and I was trying to change my life," he said.

For five years, he lived in this way, carrying people's shopping in return for bananas or plantain, and sharing what little food he had with other children.

He didn't have much hope for the future until, as a teenager a man named James befriended him after Mutabazi made a habit of helping with his shopping. James paid for Mutabazi, by then 15, to attend a small Christian school. There, he eventually thrived, sometimes borrowing richer children's books in exchange for doing their homework.

During a gap year between high school and university, Mutabazi became a relief worker, taking food and medicine to children living in Rwandan refugee camps following the genocide of the mid-1990s.

Then, after completing degrees in Uganda, the U.K. and the U.S., he became a manager at non-profit Compassion International, which raises money to sponsor children in developing countries.

Becoming a solo foster father

It wasn't until he was 43 that Mutabazi became a foster dad.

His own father was abusive, which is why he left home so young — and Mutabazi feared becoming like his dad, he wrote in his memoir "Now I Am Known: How a Street Kid Turned Foster Dad Found Acceptance and True Worth." He also thought that a single, black man would not be allowed to foster children.

"I had never seen a black person who was adopting from Uganda or from Ethiopia or from China. They were always Caucasians and married," he told CNBC.

But a conversation with a colleague — a white American man, who with his wife had fostered (and subsequently adopted) a baby, Brittany, who is black — made him re-think those assumptions.

Mutabazi also questioned how devoted he was to helping children in his role at the non-profit, and realized he wanted to do more. "I knew I was making a difference in the lives of children, but everything I did kept those children at a safe distance. I made my trips and sent my checks, and at the end of the day, I came home and closed my mind," he wrote in the book.

Mutabazi, now 49, has lived in the U.S. for 18 years. "When I came to the United States, I was really shocked to see how wealthy and how developed a country can be — but there was a divide. People just didn't know what was happening to the kids," he told CNBC.

He approached a fostering agency in Oklahoma City, where he lived, suggesting he could mentor at-risk children. But a social worker asked if he would consider fostering, and explained that he was eligible to do so as a single man.

To get approved as a foster parent, Mutabazi underwent multiple interviews and background checks and took months of classes known as MAPP — or Model Approach to Partnership in Parenting — which train foster parents in understanding children who have experienced trauma.

He found the classes helped him process his own trauma. "I didn't want my past to drag into the future," Mutabazi said of his difficult childhood. He realized: "I can really be a good dad … I can parent in the best way I can," he told CNBC. Now, on top of being a foster dad, he runs the Now I Am Known Foundation, where he does room makeovers for teenagers.

Dealing with anger

The first child Mutabazi fostered was a five-year-old boy who would sometimes have screaming fits. "One time, he cried for three hours nonstop, and at the end of it he just said, 'hey, Daddy can you hold me?'" Mutabazi told CNBC.

"Once he went into that [angry] mode, he just didn't know how to come back," Mutabazi said.

"My approach was to say, how do I help this kid regulate, control his anger, but also know that I was there for him … rather than focusing on what I was seeing, but really focusing on what was causing it really helped me to know how to parent him," he said.

The boy stayed with Mutabazi for six months before moving in with an aunt. "Even through the fits, this was a boy who just wanted to be held, and I thank God I was there for him," he wrote in his book.

Words of affirmation

When Mutabazi was living with James and his family as a teenager, he would carry a notebook and write down the positive things James said to him. "James told me I was brave for making it through all the things I'd endured in life. In fact, he said that to me a lot. Brave went in my notebook," he said in his memoir.

Mutabazi continued to write down these "words of affirmation," and this notebook became a guide for how he speaks to the children in his care. "I memorized the words: you're chosen, you matter, you're special, you're enough, you're a gift, you're not alone, and I make sure that [with] my kids, I'm going to use those words at all times," he told CNBC.

He also has the phrases printed on his steering wheel, on his fridge, in his closet, and even on his dog's tag.

The words have helped him raise his son Anthony, who came to stay with Mutabazi at 11 years old, and whom he has since adopted. Mutabazi said his son had issues with abandonment, and his approach has been one of reassurance. "That has really helped him to know, hey, my dad loves me no matter what, despite the challenges that I have," Mutabazi said.

Small wins

Celebrating smaller achievements is one way that Mutabazi shows love to the children in his care. "I come from the poorest place you could think of [and] ... I have overcome trauma in so many different ways that I do not expect my child to do the same overnight," he said.

For example, when one of the teenagers in his care struggled to make his bed, Mutabazi encouraged him to do it. "[Now] I'm able to say son, that was awesome. And I'm grateful," he told CNBC.

That also helps to reassure the children that he cares about them, so if they fail at something larger they have more faith that he loves them regardless. "I have already shown that their love and that faithfulness through the small things," he said.

Coping with teens

If other parents come to Mutabazi with questions about how to manage teenagers, he reassures them that most people struggle with kids at that age. "When you have a 14- or 15-year-old … if you put yourself as a mentor rather than a dad or mom, it helps," he said.

Try to understand your perspective of your child, Mutabazi added. "There's a teenager being a teenager, there are hormones, there's trauma, there's disrespect … when you're looking [at] your kid, look through those lenses and [say to yourself] which one am I dealing with?" he said.