The new CBSN Originals documentary, "Kid Influencers: Few Rules, Big Money," can be seen in the video player above.

Los Angeles — Like generations of child film and TV stars before them, kid influencers on social media attract the attention and fascination of audiences far and wide. But the huge growth of influencer marketing on platforms like Instagram and YouTube — expected to be a $6.5 billion to $8 billion industry by the end of 2019 — raises a world of new questions and concerns about the lack of oversight and the possible long-term impact on children's lives.

CBSN Originals spent time with some of America's most successful young influencers and their families for an intimate look at the big business of little influencers.

Taytum and Oakley Fisher

3-year-old twins Taytum and Oakley Fisher have 3 million followers on Instagram. CBS News

Three-year-old twins Taytum and Oakley Fisher recently branched out from starring in their family's YouTube channel to having a channel of their own.

It's run by parents Madison and Kyler Fisher, whose "FishFam" home-video style vlogs have amassed more than 3.6 million subscribers on YouTube. The family also has 5 million Instagram followers, of which 3 million belong to Taytum and Oakley's unique account. At just 4 months old, the newest Fisher family member, baby Halston Blake, has more than half a million Instagram followers on her account.

"(Our) new channel for Taytum and Oakley, called Taytum and Oakley Play, it's going to be more geared towards just them," dad Kyler Fisher told CBSN Originals on a recent morning at the family's Los Angeles home. "Them playing with toys or just doing whatever they do, using their imaginations and stuff like that."

Becoming a social media star is one of the most popular career aspirations named by kids in a recent survey. The influencer marketing industry is projected to grow to $15 billion by 2022. But experts warn that regulations need to be put in place as younger and younger influencers are sharing their lives on camera. Since 1939, Coogan's Law — named for child star Jackie Coogan, whose parents squandered his fortune — has protected the earnings of professional child performers. The law, however, doesn't apply to kid influencers online.

Asked about whether he's concerned about the lack of labor laws governing kids in this new social media entertainment space, Kyler Fisher said: "Who gets to say who does the work? My kids are in a picture, and that's work? I'm not so sure."

The Fishers were among the forerunners of family vlogging and can earn upwards of $200,000 per month, with money coming in from brand deals and advertising revenue from Facebook and YouTube.

Alexis and Ava McClure

The McClure family has 1.3 million followers on YouTube. CBS News

Influencer parents Ami and Justin McClure, who are friends of the Fishers, have built a small media empire around their own adorable set of twins. The McClure family has approximately 5.1 million followers on YouTube, Instagram and Facebook combined. The stars of their vlogs and posts are 6-year-old twins Alexis and Ava.

"We work hard. You've got to be very good entrepreneurs to be good at this, and you've got to be good parents, too, because you don't want to use your kids, you don't want to expose your kids," said Justin McClure. He added, "I think it's great that kids work in some capacity. So you've got to say, 'Hey, how can I run a business and also make it fun for these kids?'"

But digital media academic Karen North, director of the University of Southern California social media program and a clinical psychologist, told CBS News that child influencers' activities go well beyond the typical home videos. She's concerned about the long-term consequences of kids living their lives online for millions to see.

"The problem is the potential harm of exposing your kid's life to a huge audience so that the kids can be scrutinized and criticized," said North. "The difference between traditional child actors and social media influencers is that it's not a kid pretending to be somebody for a show; instead, the show is the kid."

"The big change when social media came in is that entertainment and interaction became very personal," she added.

Leah and Ava Clements

9-year-old twins Ava and Leah Clements are popular influencers on Instagram. CBS News

Nine-year old influencer twins and Instagram models Leah and Ava Clements said they sometimes do get mean comments, but that it doesn't ruin the fun of being an influencer. "We don't get upset, because they don't know us and our lives," the girls told CBSN Originals.

The Clements are relatively new to the influencer world, quickly gaining followers and media attention after getting their start at age 7. They mostly work with brands to promote and post their content on Instagram.

"Pretty much every day we get shipments of boxes ... from different companies that we work with, and the girls model their clothes," said Jaqi Clements, the twins' mother and de facto manager. "It's kinda crazy."

"I'm working a lot. And I'm not getting paid to manage them, so they're getting to keep all their money, which is great," she added. "Whether it's a sport or an instrument, if they're doing what they love to do, they're happy."

As for critics who tell her, "Let them be kids," she says, "That's the thing that always bothered me a little bit about that criticism ... our kids are doing what they love to do."

Instagram and YouTube respond

Both YouTube and Instagram prohibit accounts by individuals younger than 13. All of these kid influencers' accounts are run by their parents. The companies declined to be interviewed, but sent CBS News statements about young influencers featured on their platforms, which included the following:

"YouTube has always been for people 13 years of age and older and when we become aware of accounts belonging to people under 13, we immediately terminate them. In fact, we terminate thousands of accounts per week as part of this process," YouTube, which is owned by Google, said.

Instagram, which is owned by Facebook, said: "Influencer marketing continues to evolve and we're committed to working with regulators, brands, and influencers on best practices and enforcement."