向孩子们谈论性与艾滋：几岁开始？

What age is the right age to have “the talk,” not just about where babies come from, but also about sex and AIDS?

How about, oh, 4?

A new documentary, “Please Talk to Kids About AIDS,” raises this question in a cute but discomfiting way. So far it has been seen only at film festivals and at schools of public health, including those at Harvard and Johns Hopkins. But the film will soon be available at www.eztakes.com/Talk-to-Kids. I saw it last month at a Gay Men’s Health Crisis screening for AIDS counselors.

In it, two incredibly sweet and precocious sisters — Vineeta and Sevilla Hennessey, ages 6 and 4 — accompany their parents, the filmmakers, to the 2006 International AIDS Conference in Toronto. They interview top AIDS experts, gay activists, condom distributors, a sex toy saleswoman, a cross-dresser playing Queen Elizabeth II and an Indian transgender hijra in a sari.

The startling aspect is that, as one childish question leads to the next, they ask things like: “How does AIDS get into your body?” and “How come they want to have sex with each other?”

For a reporter, it is a guilty pleasure to see some of the world’s leading scientists squirm — or not — when grilled by a child.

Dr. Anthony S. Fauci, the nation’s instantly recognizable authority on everything viral, seems as relaxed as he does on television or before Congress. People get AIDS from each other, he explains in the documentary. “You know,” he says, “when a man and a woman have sexual relationships they get infected. And also from injecting from a needle that is contaminated with the virus.”

But, with children as with senators, Dr. Fauci glides casually away from the tough follow-up, segueing to: “Do you know what a virus is?”

By contrast, Dr. Mark A. Wainberg, the conference’s co-chairman, dissolves in nervous laughter.

“Well, AIDS gets into your body in ways that can — can be complicated to explain to little girls,” he says, fumbling to a finish with: “In the same way that a mommy and a daddy have a relationship that . . . results in our coming into the world. But you know what, you asked a great question. I’m just not sure I’m qualified to answer.”

The girls get straightforward answers about bodies conjoining, from Craig McClure, the AIDS society’s director, and about trading sex for money, from a prostitution-rights activist.

But the film is hardly a medical lecture. The hallway theatrics — flags, puppets, dancing — give the conference a carnival feel. In fact, an unplanned stop at the Condom Project’s table inspired the filmmakers, Brian Hennessey and Radia Daoussi, to center the film on their girls.

Sevilla thought the bright packages were candy and loved the Cinderella ball gown and tutus made of blue and pink condoms. She asked about them, and a volunteer’s struggle to turn her boilerplate spiel into words simpler than “destigmatize” made it clear that a child’s innocence would elicit good interviews.

But innocence — being fleeting — fled. At one point, Vineeta draws for the camera a picture of two people in bed. “These are condoms,” she explains of the bowl beside them, “that you put in the boy’s penis, so they don’t get AIDS with a woman or with a man. A man can do it with a man if you like it.”

Interestingly, only some interviewees checked to make sure that the producer and cameraman were Mom and Dad. To me, that would have been crucial; after all, I wouldn’t tell a child there is no Santa Claus or why I am an atheist without a parent’s permission.

The woman at the sex-worker booth did, as she was decking out the girls in feather boas for a make-believe evening on the street. “I was wondering why you were bringing kids up here,” she said to Mr. Hennessey.

Poor Dr. Wainberg said he had been swamped with running the conference and was told nothing about the girls before meeting them. “I was a bit taken aback,” he later said in a telephone interview. “I wasn’t sure if this was the time and place to go into a long explanation of the birds and the bees.”

Dr. Fauci said he had been briefed by a press aide, and guided his answers by watching the girls’ reactions. I wished I had seen more of those in the film. Were they confused? Bored? Horrified?

When the screening was over, I lingered to meet them. Would they turn out to be traumatized robots parented by publicity-seeking control freaks?

They did not. Mr. Hennessey and Ms. Daoussi are on a mission but with a sense of fun. For example, to protest cluster bombs, which kill children who find the bomblets, they staged a bomblet hunt near the last White House Easter Egg Roll.

And the girls seemed self-possessed and at ease with grown-ups. Asked by an audience member if she had any advice, Vineeta said, Yes; don’t share too much. “It’s like what they say at my school,” she explained. “Don’t share a comb or a hat because you can get lice.”

There is, Ms. Daoussi argues, no right age for the topic. “It’s when they’re ready to ask,” she said. “It’s our own discomfort that’s the problem, not theirs. Kids don’t have taboos.”

I left only partly convinced. It is possible to push very young children, with so little grasp of which fears are realistic, into information that scares them — into, for example, lying awake worrying that sex will kill their parents.

Sevilla did say she was scared twice — once by an African guerrilla theater skit showing a village massacre and an orphaned girl forced into a sugar-daddy relationship, once by learning what a sex worker did. “I know it’s a job,” she said, “but it’s a weird job.”

But the film is not really for children — certainly not in its present form, even its makers say. For a parent, however (and I have a stepson Vineeta’s age), watching someone else’s very young child — maybe even too-young child — grapple with the topic is a powerful exhortation to begin thinking about how to talk to one’s own.