No sooner had oohs been aahed over pictures of a tousle-haired Prince George arriving for his first day at the Westacre Montessori School in Norfolk last week than online parenting forums were filled with mums trying to get their hands on his natty navy jacket.

Swiftly pinpointed as a quilted number from his mother's favourite store, John Lewis, it was inundated with inquiries.

And while customers were disappointed to find that George's particular style, complete with corduroy elbow patches, hasn't been available since 2013, an almost-identical coat has had to be restocked several times. "Within the first two days we saw a 447 per cent increase in inquiries for our children's quilted, hooded jacket in navy," says a spokesman. "And that's increased 100 per cent again this week."

The fashion world now seems to be in the grip of a toddler fashion boom, led by the pint-sized prince - dubbed "the world's most influential toddler" by Forbes magazine. The UK childrenswear market is now worth £5.6 billion ($12.5 billion), according to Euromonitor, with a retail value estimated to rise to £5.9 billion by 2017, which Mintel expects to hit £7.8 billion by 2019.

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Infantswear (for baby to 3-year-olds) grew by 25 per cent between 2009 and 2014 - thought to be thanks to a strong "gifting" market.

Think Baby Boomers with disposable income to lavish on grandchildren, and a rise in older mums, who tend to be more financially secure.

AlexAndAlexa, a sleek online boutique selling 9000 lines of children's designer clothing, even recently added a luxury ski store.

Surprisingly (or worryingly), some of the under-3s at the front of the fashion pack are even dressing themselves. "When it comes to toddlerwear, children are developing a sense of style and often outfit choices will be a combination of the parents and the child's choice," says Jenny Slungaard, PR manager for AlexAndAlexa, which was set up seven years ago by parents-of-five Alex and Alexa Theophanous.

"With the rise of social media, particularly Instagram, parents are becoming a lot more conscious about what children wear - as are the kids themselves."

The Duke and Duchess of Cambridge with their two children, Prince George and Princess Charlotte. Photo / Kensington Palace
The Duke and Duchess of Cambridge with their two children, Prince George and Princess Charlotte. Photo / Kensington Palace

For AlexAndAlexa, (former toddler) Harper Beckham remains the site's "key trend driver", with that floppy Chloe hat sending it into meltdown. "She wears so many of the pieces we stock and we always see sales increase as soon as she's been photographed in them," says Slungaard.

But no toddler drives more sales than George: from the Start-Rite shoes he wore in his first Christmas snaps, to the nautical-style Crocs he was spotted playing in at the polo last year.

Although his quilted jacket has been setting trends, its vintage, however, suggests the little prince has been kitted out in the most affordable toddler gear of all - a hand-me-down.

William's stepsister Laura Lopes (daughter of Camilla Parker Bowles) whose twin boys, Gus and Louis, would have been wearing that size when the jacket was on sale back in 2013, is an obvious contender for purchasing the original.

But even in this Prince George is ahead of the curve because hand-me-down, or secondhand, children's clothing is big business online, too.

One mini fashionista more likely to be spotted in couture than cast-offs is Kim Kardashian and Kanye West's daughter, North. Her wardrobe reads like a who's who of fashion: Balmain, Givenchy, Celine, Balenciaga. Last year, she caused a Kardashian-esque uproar when she was spotted in a US$3500 fur coat, leggings and Doc Martens boots after Daddy's adidas fashion show in New York.

After pictures of Princess Charlotte were released in November, AlexAndAlexa reported "an explosion" of searches for pale pink cardigans and floral dresses.

Retailers must be counting down the days to her nursery debut, in September 2018.