What do billionaires Jeff Bezos, Mark Cuban and Richard Branson have in common?

They each started their first business before graduating high school.

Stories of 20-somethings launching start-ups from their dorm rooms seem to pop up everywhere, but it seems entrepreneurs are getting even younger.

While they aren't billionaires yet, these eight entrepreneurs under 18 years old are making a name for themselves—and some serious cash.

—By CNBC's Sarah Whitten
Posted 27 July 2015

He's only 7, but he's already CEO of his own company and a philanthropist.

Sebastian Martinez's passion for collecting bright and zany socks turned into a business when his mother suggested he design his own. The result was a company called Are You Kidding which Sebastian started at age 5.

In 2014, Sebastian made $15,000 selling his specialty socks with the help of his director of sales and big brother Brandon Martinez.

Since January revenue has continued to grow. "We have been able to already reach the $15,000 that we made last year and are on track to double and hopefully triple our sales this year," Rachel Martinez, the president of the company and Sebastian's mother, told CNBC.

Are You Kidding teamed up with organizations like the American Cancer Society and the Live Like Bella Foundation last year to raise more than $3,000 for cancer awareness. In April, the company partnered with The Hue Studio and donated 25 percent of all proceeds from its "Eye See You" sock sales to Discovery Arts, a charitable organization that brings art programs to children with serious illnesses.

What is it like to be a millionaire before you even hit puberty? Just ask 9-year-old Evan from EvanTubeHD.

The face of the highly successful YouTube channel, Evan has been reviewing toys and building Lego sets online since he was 5, and it's a staggeringly big business.

This pint-sized entrepreneur has three channels on the video platform and more than 2.8 million subscribers. He has amassed more than 1.9 billion views on the platform and is estimated to make $1.3 million a year.

"We've already maxed out certain accounts, so I think the college education is pretty much taken care of thank goodness," Jared, Evan's father, told NBC News in December. The father has not disclosed their family name.

Nine-year-old entrepreneur Alina Morse had a pretty sweet idea in 2014: create a sugar-free lollipop that tastes good and is good for you.

With a little help from her father and a lot of research, Zollipops was born.

These clean teeth pops are made with sweeteners xylitol, erythritol, stevia and other natural ingredients and help to neutralize acidity in the mouth, so the bacteria that causes tooth decay cannot grow.

Last year, Alina racked up $70,000 in sales and was featured on the kids' edition of "Shark Tank." She's now working to get Zollipops into dentist offices and schools across America.

At 13, Moziah Bridges is well on his way to becoming a fashion mogul.

This dapper CEO launched his bow-tie business, Mo's Bows at age 9 and catapulted into the spotlight after becoming the youngest entrepreneur to appear on "Shark Tank."

His company made $350,000 in sales since 2011 and is expected to earn $250,000 in revenue for 2015, mother-manager Tramica Bridges told CNBC via email.

Bridge's collection is sold in shops and boutiques in six states and in his online store.

Web designer and entrepreneur Zachary Weisenthal may only be 14, but he's already the driving force behind two companies.

The young CEO was inspired to launch Zach's Web Designs in 2014 after attending the entrepreneurial Maverick Family Freedom Event with his father.

Zachary has built customizable websites for a variety of businesses, including Keep Punching, a nonprofit brain cancer organization, Ry's Ruffery, an all-natural dog biscuit company, and Emilee Tominovich Racing, the official website of an up-and-coming female race-car driver.

The company has generated $15,000 in revenue since its inception.

His newest venture, Serpent Skating, is a sports merchandise business specializing in laser-engraved skateboards. The enterprise is set to launch on Kickstarter this year.

Gladiator Lacrosse was established in 2013 by then 13-year-old Rachel Zietz, an entrepreneur and lacrosse player, who found sports equipment too expensive and not particularly durable.

After attending the Young Entrepreneurs Academy in Boca Raton, Florida, she pitched her concept to investors and was awarded $2,700 toward development. She has since created a line of quality and affordable rebounders and practice goals for lacrosse players.

In the company's first year, Rachel's company had $200,000 in sales. Two years later, Gladiator Lacrosse has generated more than $1 million in revenue.

Most recently, the young executive was honored as one of the finalists for the Greater Miami Chamber of Commerce's 2015 Entrepreneur Award.

Noa Mintz is a freshman in high school and she already makes more money than you do.

At 12 she launched Nannies by Noa, a full-service childcare agency. Three years later, her business services 190 clients in New York City with a network of 150 sitters and nannies.

"I knew what kids wanted in a nanny. I had the unique perspective." Noa said in an interview in February. "So I set out to start with a couple family friends. Then people thought it was a really good idea to have a kid helping them. And trust for the brand grew."

Noa does not disclose her company's financial information, but she said Nannies by Noa charges a standard 15 percent of a nanny's initial annual salary. For baby-sitting services, clients are charged a flat-rate of $5 per hour.

Stinky Feet Gurlz, a 1940s-inspired apparel and accessory company, was founded by Asya Gonzalez at age 14. Three years later, the recent high school graduate is in the process of developing a new clothing line, which delves into winter sports wear, and prepping for her freshman year at the University of Denver.

Gonzalez, 18, told CNBC she estimates that her company's sales will reach $7,000 to $10,000 a month with the addition of the new line of apparel.

In addition to her business, Gonzalez runs her own charity, She Is Worth It, which is dedicated to fighting sex trafficking of children. A portion of all sales from Stinky Feet Gurlz goes directly to this organization.

Most recently, Gonzalez was honored by the National Federation of Independent Business with the Dan Danner Leadership Award. For her entrepreneurial efforts, Gonzalez also received a $15,000 scholarship from the organization.