Britain's Princess Charlotte and her brother Prince Louis are seen in this handout photograph taken by Britain's Catherine, Duchess of Cambridge, at Kensington Palace in London. Picture: Reuters

London - She's known to reuse her own outfits. And the thrifty Duchess of Cambridge is doing the same with the clothes of her three young children.

In photos of the new royal baby taken by his mother, Prince Louis is wearing a cream jumper and legging set that his big sister wore as an infant for her own first portrait.

The matching set by Irulea is now called the Princess Charlotte set. Louis, two weeks old today, is pictured propped up on a white frilly cushion on a seat at the family residence in London.

In another image, Charlotte carefully cradles her brother while planting a tender kiss on his head. She is wearing a navy blue cardigan by royal favourite Fina Ejerique which her brother George wore for a Vanity Fair family portrait celebrating his great-grandmother the Queen’s 90th birthday.

READ: British royal family releases first official photographs of Prince Louis

The touching images were taken on May 2 – Charlotte’s third birthday. George, four, is missing from the photos, possibly because he was at school at the time.

Britain's Prince Louis is seen in this handout photograph taken by Britain's Catherine, Duchess of Cambridge, at Kensington Palace in London. Picture: Reuters

It is not the first time Kate, 36, has put her children in hand-me-downs. Charlotte has previously worn another of George’s cardigans, while he once wore a pair of shorts and a shirt first worn by his father Prince William in 1984.

Charlotte has also worn a pair of red buckled shoes that her uncle Prince Harry wore as a child in 1986.

Kate, a keen photographer, has frequently released pictures of her children at landmark moments in their lives.