When I arrived at its London office it was evening and the children, who are the agency's reporters, were arriving from school for a few hours' work on the stories to which they had been assigned. On the wall was a gigantic whiteboard with the week's stories listed on it and the names of reporters covering them.
Clency Lebrasse, aged 15, was listing questions he wanted to put to Graham Kelly, Football Association chief executive, at an interview he had arranged for the following week. It was clear that Mr Kelly was not going to have an easy time. "I want to ask him how he is going to sort out football before next season. Basically I want to look into how he's going to stop kids picking up on the bad habits of their idols," he said.
Elsewhere, Kathleen Dawes, aged 14, was working with two other reporters on a VE Day anniversary story. Their job was to interview an artist who had done some atmospheric drawings of the 1945 VE Day celebrations. Having recently suffered the journalist's nightmare of the unresponsive interviewee, they were a bit worried that she wouldn't be nice to them, but were anxious to get her to discuss her feelings about the war.
Bureau chief, Cathryn Atkinson, had led them through a revision exercise on interviewing techniques. Apart from the basic who, what, where, why and how questions, she encouraged them to think of some "man from Mars questions", those that assume no knowledge at all on the part of the reader. She reminded them that devil's advocate questions can provoke strong quotes.
Newspapers were energetically being combed for background material, and Cathryn Atkinson was kept busy answering questions about subjects ranging from Hiroshima to fire bombs. The amount of learning taking place was impressive.
But the interview went well and the story, credited to both the agency and the individual reporters, appeared in the Independent on Sunday this month.
Children's Express was set up in the United States in l975. Originally a magazine produced by adults for children, it was decided that the children would take over when child writers, acting on their own initiative, scooped the news of Walter Mondale's vice-presidential nomination.
Although articles are edited by adults at the final stage to allow them to appear in reputable newspapers and magazines, the aim is to offer a child's perspective on events. "It is extremely important", says Cathryn Atkinson, that "the voice of the children comes through clearly in the printed piece".
A charity supported by organisations including the Prince's Trust, the Gulbenkian Foundation and the Reuters Foundation, Children's Express was launched last year with a pilot scheme involving 30 children, chosen on the basis of enthusiasm rather than ability. Four teenage editors from the New York bureau were flown to London to help with their training.
"The hardest thing for them to grasp is that they are not writing an essay for the teachers, but trying to hold a conversation with thousands of people, " says Cathryn Atkinson.
The bureau operates like a club, with 40 children at present working as journalists, a figure that will eventually rise to 150.
Children work at the agency in the evenings, during holidays and on Saturdays, and are generally expected to follow a story through. Otherwise it is recognised that other commitments may get in the way of their attendance.
They work in teams of about five and all interviews are tape recorded and fully transcribed, both to ensure accuracy and to enable the children to concentrate on asking questions.
Children's Express journalists don't dodge tough stories and already they have tackled interviews with the British National Party, a teenage mother and four young offenders.
And the interviewers don't beat about the bush. "When did you first find out about sex?" and "What would you do if your daughter became pregnant?" were among questions fired at Kenneth Calman, chief medical adviser at the Department of Health.
But will the stories sell? For Children's Express is not just an exercise a children's voice in our national newspapers is the goal. Cathryn Atkinson admits that there has been considerable cynicism from some newspapers as to what "a bunch of kids" can offer, but is adamant that "We want to be known for quality. This is a serious idea before it is a nice idea."
Children's Express London Bureau, Exmouth House, 3-11 Pine Street, London EC1 OJH. Tel 0171 833 2577.