An entrepreneur has engineered a sandal, called The Shoe That Grows, that expands with a child in order to prevent them from growing out of them so quickly. It's an incredible idea no matter where you live, but it's particularly important in countries such as Kenya, where many families can't afford to replace shoes every couple of months.

Children's feet grow really fast - between the ages of two and six, they can go up a size every couple of months, and by the age of 10, most children have completed between 80-90 percent of their foot growth. Because of this, there are an estimated 300 million children around the world who don't have access to shoes, according to The Shoe That Grows website, and many more who wear shoes that don't fit. Not only can this lead to pain and abnormal development, it can also expose kids to soil-transmitted disease and parasites.

Kenton Lee, the inventor of The Shoe That Grows and the founder of charity group Because International, was inspired after working in an orphanage in Nairobi, Kenya.

"I'll never forget it," Lee told the Daily Mail. One day I was walking down a road with a group of kids from an orphanage where I was staying. Next to me there was a girl in a white dress. As I looked down her shoes were so small and as I looked around there were so many other kids with shoes that were too small for them."

The Shoe That Grows is made up of durable leather, a compressed rubber sole, and metal buckles that allow the shoe expand in three places - the front, sides and back. This means it can last the average child five years.

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But although Lee knew what he wanted to create, putting it into practice was slightly harder - not only did he have to make a shoe that would fit a wide variety of foot shapes, it also had to be durable enough to grow with a child.

In order to develop the product, Lee partnered with Gary Pitman, a footwear designer who had formerly worked with Nike and Adidas, and the team used 3D printers to model a range of different feet. The shoes are currently available in two sizes: small, which is designed to last from kindergarten age up until around Grade Four, and then the large, which aims to take kids from Grade Five to Grade Nine.

The team is also doing their best to keep the cost down, with each pair of shoes costing around US$30 on their own, or US$12 in a pack of 100. Lee has told BuzzFeed that around 2,500 kids have received the shoes already, and they're hoping to produce their next batch soon.

Find out more in the video below: