Children are stars of London's Chelsea Flower Show

Children got a starring role at London's Chelsea Flower show, which opened to the public Tuesday, with a "no adults allowed" garden and a chance to judge six of the biggest showcases.

The five-day horticultural extravaganza, which expects over 150,000 visitors between now and Saturday, does not allow entry for under-fives and has a policy of charging older children full price, which is enough to deter most families.

But the tide appears to be turning with school children this year invited to design their own garden.

King Charles III, a passionate environmentalist, and Queen Camilla on Monday got a preview of the "RHS No Adults Allowed Garden", where the amused monarch was presented with a "King of the Compost" badge while Camilla received one with "Queen of the Bees".

"There's nothing more fun than eating the things you have grown... It tastes so much better," Charles said as he toured the feature.

Designed by 29 pupils from a west London primary school with the help of landscaper Harry Holding, the garden will be partially reinstalled at their school after the show ends.

Holding, 30, said he believed gardening should be part of the school curriculum.

"Bringing children into that conversation is absolutely vital... in a rapidly changing world where horticulture, gardening and environmentally conscious activities to do with landscape are more and more important," he said.

Working alongside nine and 10 year olds with their powers of imagination going at full throttle, however, also brought its challenges.

Some of their ideas were "very fantastical, very magical", he said.

"Some sort of den, with hidden doors, trap doors and tree houses... They wanted a crocodile... a lot of ideas were very big, like rivers and lakes," he recalled.

The body of water came into being, in a much more compact form. The crocodile, thankfully perhaps, remains a project for another day.

"The great thing about working with children is that they are really uninhibited by industry norms and how you should do things that really allows the creativity just to run wild," he said.

From this joyful creativity came a garden with a slide descending into a small pool, a tree house resembling a den at water level, rocks to climb on, a mini woodland, meadow and wetland.

Also featured were oversized tropical plants in bright colours and carnivorous ones in which the children were very interested.