"The kids in Spain are always immaculate – it's traditional, but the cut is little bit more modern," says children's wear designer Amaia Arrieta
Credit: Tim Rooke/Rex Shutterstock; HRH The Duchess of Cambridge/Getty

Christmas came early for the European children’s wear brands that scored a surprise appearance in Princess Charlotte‘s first solo portraits.

The m&h floral-print cotton dress with smocking effect and frill collar, a style very popular for young babies in Spain, is believed to have been bought by nanny Maria Turrion Borrallo. It has since sold out, but designer Margarita Pato Cid is working to restock.

“We’ll receive more in a couple of weeks, but due to the success of the photographs, they are all reserved,” Cid, whose flagship store is based in Madrid, tells PEOPLE.

“We love the way Kate has dressed her children for public events – it’s a very classic, elegant way, with a European style we identify with,” adds Cid.

The cotton dress cost just $32, but it was paired with a luxurious cashmere cardigan (still unidentified) and pale pink ribbed tights from upscale London boutique Amaia, a favorite of Princess Kate‘s located in Chelsea Green.

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“I think it’s nice that Kate chose a dress from a really small brand that nobody knows,” Amaia Arrieta, owner of the eponymous boutique, tells PEOPLE, adding that the style was far from surprising: “The kids in Spain are always immaculate and it does have a great reputation for kids’ fashion – it’s traditional, but the cut is little bit more modern, which I think she likes.”

With a clear love of Spanish kids’ clothing (not only is Amaia herself Spanish-born, but Kate exclusively dressed Charlotte in high-end Spanish children’s wear and home goods boutique Irulea for every public appearance so far, except the christening), it’s clear that nanny Maria is having a sartorial influence.

“I think the nanny understands what Kate likes, and she is happy for her to buy things – it’s easier because it’s more discreet, says Arrieta, whose sock sales have been booming ever since Prince George became a fan of her cotton knee-highs.

And it seems that Kate s love of European children’s wear also extends to Italy as Kate, her sister Pippa and Maria have all bought items from the Italian cashmere brand Love In Kyé, stocked at both Nursery Window and Trotters, two of Kate’s go-to shops in London’s Chelsea neighborhood. They even made some bespoke items for George when his size wasn’t available.

With reporting by NINA BIDDLE