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?”