Thirteen-year-old JoJo Siwa rolls up to school in a souped-up vintage car with a giant pink bow plastered on the grille.

Inside the car, with her blond hair tightly pulled into a side ponytail and wrapped in a pastel yellow bow, she sings to her mother, “I don’t really care about what they say,” while a group of mean girls wearing not-so-pastel clothes snickers from a bench.

(We know they’re mean girls because the words “mean girls” are displayed on the screen next to them.)

“Don’t let the haters get their way,” JoJo’s mother says.

No worries.

The new young teenage heroine of suburban America shows no fear in her video Boomerang. After winning a rowdy dance battle, JoJo places a purple bow on the lead mean girl. Everyone becomes best friends.

Thirteen-year-old girls aren’t generally known for their oversize bows these days, but JoJo isn’t your typical teenager. The YouTube star, who has 2.7 million subscribers, just signed a multiplatform deal with Nickelodeon, which includes consumer products, original programming, social media, live events and music.

“I’m 13, and I like being 13,” JoJo said in a recent interview. “A lot of people my age try to act 16. But just be your age. There’s always time to grow older. You can never grow younger.”

In a world where parents of children ages 8 to 14 have long been concerned about hypersexualized clothing, early puberty and overly sophisticated media messages, JoJo is part of a growing group of girls documenting routine, age-appropriate behaviors and activities such as being nice, doing their chores, divulging what’s in their backpacks, making dresses out of garbage bags and working to pay for their own clothes.

The 12-year-old competitive gymnast Annie LeBlanc, aka Acroanna, has had a YouTube channel since she was 3. On her channel, which as been viewed a combined 174 million times, Annie documents herself making slime blindfolded and investigates what’s in her purse.

She appears on her family’s online channel, Bratayley, where 3.9 million subscribers follow her, her parents and her 8-year-old sister, Hayley.

Many popular videos made by girls in the pre- and early teenage years live on nine connected YouTube channels. Seven Super Girls, the most successful of these channels, has over 6 million subscribers.

The channels were started in 2008 by seven families in Britain who, in the early days of YouTube, wanted to make sure their children were making family-appropriate content.

Alexis, a 12-year-old from Southern California, has made close to 200 videos for two of the channels, Seven Cool Tweens and Seven Awesome Kids, over the past three years.

Alexis wears her reddish-brown hair in a braid, no makeup and braces. Her bedroom isn’t catalog perfect. Her most popular videos revolve around silly antics like pranking family members, making a mess of herself and her outfit before the school dance and getting grounded for life.

The appeal?

“Kids want to watch kids,” Alexis said in a phone interview.

Twelve-year-old Emily — a screen name — of the channel Seven Awesome Kids is home-schooled in Southern California. Some of her most popular videos include walking through a mysterious forest and finding an angel potion.

“She’s a little Stanley Kubrick, controlling everything,” said her father, Tim Gould.

While Alexis has received money from the channel, Emily has not.

The parents seemed ambivalent about the arrangement — knowing that allowing their children to have an online identity comes with risks of harassment or worse.

But they don’t want to stop their daughters from realizing dreams of becoming a director or an editor or a writer. Or a television star.

Despite the wholesome activities depicted in the preteen videos, the YouTube trend is disconcerting for some people, like Emily Long, the director of communications and development at the Lamp, a media-based literary group.

“It’s troublesome to me when I see this being celebrated as the herald of what our young girls should aspire to,” Long said. “That you, too, can go from being a YouTube star to having your own deal on Nickelodeon.”

She would like to see girls being recognized for more thoughtful content, she said, such as that of Marley Dias, 12, who started the #1000BlackGirlBooks campaign last year after recognizing a scarcity of young, black female protagonists.

“If I had a 13-year-old,” Long said, “I would push her toward someone like Marley Dias instead of JoJo.

“Marley Dias doesn’t sell giant hair bows,” Long said. “Marley Dias sells social justice and social causes and writing and nerd culture. And there’s plenty to market there.”