It's official: Legos aren't just for kids anymore. In the last decade, Lego has doubled its revenues by developing increasingly elaborate - and more expensive - sets aimed at adult customers - and they're not the only ones doing it in the toy world.

There are even those willing to spend hundreds on a single product from the iconic company. The Star Wars Millennium Falcon set is on sale for €849 on Lego's official website; a Liebherr excavator costs as much as €1,200.

"These days, it's not just for geeks, " defends a Lego builder for adults in a conversation with The Wall Street Journal. "We don't buy every new set that comes out. We also have to eat," says another toy lover.

"We decided to focus on adults because we realized that we had a much bigger opportunity than we were taking advantage of," said Julia Goldin, Lego's product and marketing leader. It was a change of strategy that has paid off: the company has doubled its revenue in the last decade to around 9.4 billion euros by 2023.

The trend is not new: adults really do seem to like it and are willing to spend their money on products that used to be exclusively associated with children.

The Barbie movie is a glaring example: it made over a billion euros at the box office, Warner Bros' biggest hit; Hasbro, another toy giant, has also taken the classic board games Scrabble and Trivial Pursuit and reformulated them into an adult version.

The secret may lie in nostalgia - or perhaps many of us still have a child inside.