Flynn may be 10 years old, but he already has a signature style.

“I like to dress up,” the Philly-based fourth-grader tells The Post, padding around the powder-blue rooms of the Madison Avenue Brooks Brothers as he tries on one dress-slacks-and-blazer combo after another. “I take pride in fancy stuff. J.Crew is too much casual-ness …

“Most kids are going to wear [sweats],” he adds, “but to be honest, sometimes I feel underdressed in jeans and a polo shirt.”

While he trusts his own impeccable taste, Flynn agreed to let stylist and personal shopper Mona Sharaf help him find the “classic” clothes he was looking for.

As Sharaf recalls it, Flynn’s mother hired her, saying, “My son dresses too old.” And so the Manhattan-based stylist guided Flynn through a daylong shopping spree that yielded more than $2,000 worth of clothing, including an $800 navy suit and $400 blazer from Peter Elliot and $200 Italian nubuck Michael Pasinkoff leather loafers with a more youthful buckle.

And that didn’t include Sharaf’s $200-per-hour fee.

No longer a mainstay of the rich and famous, personal shoppers and stylists now cater to an increasingly diverse clientele — some of them in elementary school. Stylists say most of these kiddie clotheshorses simply refuse to endure another tense shopping trip to the mall with parents who just don’t understand.

Even so, Sharaf, who has been a stylist for six years, was taken by surprise this summer when she found herself working with five kids, ages 10 to 17, on their upcoming wardrobes.

“Kids have their own idea of style,” she tells The Post. “Parents don’t tell their kids what to wear the way we were told when I was growing up. The kids call the shots now.”

Granted, Flynn’s grandfather — who footed the bill — was dubious at first, thinking it would spoil him. “Even though I thought it was ridiculous, it worked out great,” the grandfather, a Philadelphia businessman, says now. “He’s loved to get dressed up since he was 3. It’s my job to expose him [to clothing], and it’s his job to decide.”

Image consultant Amanda Sanders says New York City kids in particular “want to express their individuality.”

That said, adds Sanders — whose newest client is 3 years old — they sometimes need help.

“They want to pick up pieces from Lester’s, Bloomie’s and Barneys and have someone put it together for them,” says the stylist, who charges $350 an hour and requires a minimum of three hours.

She says her 3-year-old client is being prepped for interviews at preschools, a process that also involves thousands of dollars of coaching.

“The mom says, ‘We need to look the part,’” Sanders recalls. “The school interview process in Manhattan is incredibly competitive — it’s not insane to work with a stylist.”

She takes her young clients everywhere, from street-savvy downtown stores such as Flight Club to kids’ mecca Lester’s to Barneys, where some parents have their credit cards on file to pay for their spawn’s $300 Gucci sneakers, $800 Moncler jackets and $1,000 Yves Saint Laurent or Prada backpacks.

“Logos and knapsacks are hot for kids,” Sanders notes.

She and other stylists say it’s gratifying to help groom future fashionistas, claiming that a strong personal style builds poise.

“It’s great working with kids because you can teach them at an early age that they don’t have to dress like everyone else to be cool,” says Lauren Rae Levy, a celebrity fashion stylist and personal shopper. “Dressing for yourself and wearing what suits you best is always the coolest. Then you can show them that wearing their confidence is their best accessory.”

Young Upper West Siders Ella, 12, and her brother, David, 10, have been honing their personal style for the past year, with Sanders’ help.

“When Amanda picks out the clothes, it’s more unique and trendy — it’s that perfect combination,” says Ella, who can sometimes clash with her mom when they shop together.

“I don’t always like what she picks out,” the seventh-grader says. “She doesn’t get my style.”

And that, says Sanders, is where stylists come in handy, acting as buffer zones in the mother-child shopping wars.

“Parents don’t want to stand there screaming with their kid over an inappropriate outfit,” she says. “After a summer growth spurt, it can be a whole new body they don’t know what to do with — and sometimes the parents want nothing to do with it.”

Although it’s usually parents who do the hiring, some kids take the initiative themselves, often by Googling “stylist” or “personal shopper.”

Sanders says she’s heard from youngsters who’ve told her, “I don’t fit in, I’m not comfortable and I want to look cool going back to school.”

For Jackson, a 14-year-old Upper East Sider, retaining a personal shopper who understands his ice-hockey-playing vibe was a no-brainer.

“I respect her point of view,” he says of Sanders, whom his mother hired as a stylish sounding board while he shops for Supreme, Off-White, Yeezy sneakers and other favorite brands.

“I don’t know what looks good on me,” Jackson says. “She’s my second mirror.”