Experts suggest a number of reasons for the popularity of the trend:

- Playfulness taps into a fun, stress-free era, escaping current problems and uncertainties.

- It draws on our collective memory of the past, connecting us through a sense of           collaboration.

- It brings out our 'inner child', making us feel youthful and energised.

- It embraces creativity, humour and optimism.

- It is spontaneous and interactive, releasing us from 'grown-up rules' and structures.

Trend forecaster Scarlet Opus describes the 'play trend' as being about a yearning for freedom and a desire for community and a more sharing society.

Children learn a range of social and communication skills through play - but what about adults? Studies show that being playful can have similar benefits for our general wellbeing, cognitive skills, and even our relationships.

At work, playful behaviours can boost productivity and creativity. Google and Facebook weren’t just messing around when they introduced slides, treehouses and hammocks into the workplace.

But as more and more leisure venues get on board with 'infantilising' activities for adults, are we taking a baby step too far? Instead of improving our reality, are we trying to deny or escape it?

All sorts of places offer us the chance to forget our adult worries and responsibilities. Regression Sessions, a retro-themed club night that brings all the fun of space-hoppers and face paints to the nightclub experience, "demands that punters leave any sense of being a grown-up at the door". Wacky World, which organises adults-only inflatable activity sessions, invites you to "forget the bills" and "be a kid again".

As trend and innovation website TrendHunter.com notes, playful product packaging and presentation can elicit a strong emotional reaction, allowing "adult consumers to reconnect with their youth".

Whether it is used to sell products or simply to create a playful experience, these sorts of visual cue are important. Camille Walala, a graphic artist who installed an inflatable castle near Liverpool Street Station for London Design Festival 2017, also uses design as a route to playfulness - something she believes is "as important for adults as it is for kids".

Describing another interactive art installation in London’s Now Gallery, Walala says she wanted to encourage people to "find their inner child". An immersive maze, it uses mirrors to play with visitors’ sense of perspective.

And it’s official: big kids are big business. No wonder Smyths Toys Superstores recently announced it was opening a Big Kids’ Aisle; NPD Group has reported that the UK 'kidult' toy market is growing three times faster than the toy sector overall.

Adult colouring books continue to flourish, perhaps because of their associations with mindfulness and relaxation in a technology-heavy age. We already know that play has a positive effect on our wellbeing - reducing stress and allowing us to live in the moment.

But it seems there may be even bigger benefits for mental health than first suspected. 

One recent study suggests that colouring-in can reduce symptoms of depression and anxiety in as little as 10 minutes a day. Business may be booming, but consumers may be the real winners.

And if colouring-in sounds like child’s play to you, remember the words of George Bernard Shaw: "We don’t stop playing because we grow old; we grow old because we stop playing."