If there's anything that would kill me, it is waking up in the morning with nothing to do

Nelson Mandela

As he settled down to take questions from readers of BBC News Online and listeners to BBC World Service, he was relaxed and smiling.

His wife, the equally impressive Graca Machel, was at his side to join him in a unique webcast and radio programme to preview the UN special session on children which is to be held in New York next month.

Little smiles

They rarely appear together these days - both are indefatigable campaigners - yet here they were, seated side by side in his office at the Nelson Mandela Foundation in Johannesburg, frequently exchanging little smiles and often touching each other's hands fondly as the recording got under way.

Mandela himself walks with some difficulty now, yet his mind is as sharp as ever.

He responded to listeners' questions, and added his perspective to Mrs Machel's answers.

Mandela's shirts are not for sale

We'd been warned that he has some hearing difficulties these days, but he seemed to have no difficulty in fielding questions from all four corners of the globe.

How could black Americans help bridge the digital divide to help African children gain access to the internet? he was asked.

And, quick as a flash, he passed it straight to his wife. "She's the expert on this," he smiled. "She's been on a computer course."

"That's not fair," she protested, and then went on to give a comprehensive reply to the caller.

Workaholic

Where do you get your wonderful shirts? asked an e-mail. And are they for sale?

"They are given to me as presents," was the reply. "I can't remember a single occasion when I bought a shirt. And if the young man from the States wants to send me a shirt, he is free to do so."

And why doesn't he retire, asked another e-mail. Doesn't he deserve a quieter life?

He enjoys what he does, especially after he retired from government, he's not doing things he's told to do. He chooses what to do

Graca Machel

"I'm sure I do", said Mr Mandela with a smile. "But if there's anything that would kill me, it is waking up in the morning with nothing to do."

I asked Mrs Machel if she'd ever tried to persuade him to do less.

"I made that mistake," she said. "But he enjoys what he does, especially after he retired from government, he's not doing things he's told to do. He chooses what to do."

Protecting children

But apart from the personal questions, both Nelson Mandela and Graca Machel wanted to concentrate on the forthcoming UN special session.

They are convinced, they say, that the world's political leaders can, and should, do more to protect children from war, disease, and poverty.

Graca Machel is the family's computing expert

A teenage Afghani girl living in a refugee camp in Pakistan sent in a video question: What about children in Afghanistan, she asked, who are dying of hunger because of economic sanctions?

Yes, said Mr Mandela, sanctions can be useful when it is necessary to put pressure on a government which fails to observe basic human rights (sanctions, did after all, play a part in the pro-democracy struggle here in South Africa), but not sanctions which harm children.

In the case of Afghanistan, targeted sanctions should be imposed in place of comprehensive sanctions.

Education is the key

Time and again, he returned to the importance of education as way of helping children move out of poverty.

As for politicians, they must find ways to resolve their differences without going to war - and they must do more to be honest about the scourge of Aids.

They must be honest about what needs to be done, and honest in talking about it.

And then it was over. Handshakes all round, a group photograph on the porch, and then back inside for the next meeting.

Not bad for a man now in his eighties who spent more than 26 years in prison.