The redoubtable environmentalist had already had the girls from St Joseph's RC independent day school in Kenilworth, near Warwick, acting out trees, arctic terns, sea anemone and walruses in a lively demonstration of the interdependence of all living things.
Now, he needed frogs. "I've just written a book called Bellamy's Big Book of Poo," he says. "It goes down the River Avon, and all the frogs say, 'Kenilworth poo is coming along'."
He asked the girls what they had for supper one day that week, and compiled a list of food from all over the world: lamb from New Zealand, oranges from Zimbabwe, rice from India, beef from Argentina, corn from Russia. "We take all these goodies from all over the world and what are we doing?" he asks. "Flushing them down the loo." Three main nutrients - K (potassium), N (nitrate) and P (phosphate - "and P for poo as well") all go down the toilet. Meanwhile, the frogs choke and the salmon can't get up the Severn to lay their eggs. "Everything we do changes the world," is his message.
The setting for this lively workshop was Disneyland Paris, where primary children from 26 countries gathered last month for what was ambitiously called a children's summit on the environment, taking its cue from the adult one in Rio de Janeiro in 1992.
Organised by Disney Magazines in co-operation with Unesco, the event's immediate outcome was a children's charter for the environment. Presented to Federico Mayor, Unesco's director general, at a ceremony for the 700 children at the organisation's Paris headquarters, it called on the world's powers to "make the air pure", "save our oceans", "promote education to change our way of life" and "ensure peace in the world for a secure tomorrow".
Disney itself boasts about "green management", including recycling policies, environmentally sensitive landscaping, use of alternative fuels, and, in the United States, "a system for managing used water and organic residue".
In addition to the privilege of a workshop with David Bellamy, the Kenilworth children had the chance to visit Unesco, lead the Disney character parade through the famous amusement park and, of course, go on the rides.
Pierre Sissman, president of Disney consumer products in Europe, Africa and the Middle East, says that through the Children's Summit and the charter, Disney has been able to give children a voice. Disney magazines in Europe have 47 million readers and much of their mail expressed children's interest in the environment. He admits the ideas in the charter are not original, but says, "the fact that children have thought of this is important," and it was going to all 180 delegates to Unesco. "What they will do with it I have no idea. "
But the three-day event wasn't exactly a summit - there was little opportunity for the 10 girls from St Joseph's to meet their peers from the other countries, which ranged from South Africa to Slovenia, Spain to the Arabian Gulf states, let alone exchange weighty ideas. The charter, apparently, was pretty much drafted in advance, based on the children's interests.
The main "work" of the conference consisted of three-hour workshops for each national group of children, with a leading environmentalist from their country. Each group focused on a different issue - England's was wildlife conservation, and others had titles like animals, oceans, energy saving and recycling - and were meant to decide what they would do about these things in their local areas when they got back home.
In addition to writing the poo letter, followed by visits to the Severn Trent cleansing plants, the Kenilworth children will be improving the school's links with the Warwickshire Nature Conservancy Council and its work maintaining the common behind their campus. Their form tutor, Noreen Thornhill, says she will be taking these themes up in a major way in the autumn term, and that the children will also contact local industries to see how they "use or abuse the local brook".
But links between schools were being established only in the aftermath of the summit, Disney's second. Mrs Thornhill was also inspired to investigate links with Peace Child International, for young people aged 10 to 18, which offers them the opportunity to exchange information and ideas on environmental issues, and she plans to use their children's edition of the Rio Earth Summit's agenda with her pupils next term.
St Joseph's Year 5 class won the trip to Disneyland by entering a poster competition organised by Scholastic, which runs Disney Book Clubs in the UK. Their bright vision of a perfect world, made of entirely recycled materials, beat 1,100 other entries. The girls prepared for the event by researching a topic of their choice - such as frogs or whales - in addition to their environmental studies work.
David Bellamy saw the children's summit as a chance to give young people "a thought that they do affect the whole world".
To those who see Disney and ecology as antithetical, he says: "This is eco-tourism at its best." In other words, Disney parks are ecologically well-managed, and also keep tourists away from natural beauty spots which are gradually being ruined by too many visitors. But, he stops to wonder, "What happens to the poo here?"