For a politician, prodding your children into the hot glare of the media is like tossing a chip on to a roulette table. Sure, you might win some handy publicity if your children are cute enough. But the odds are stacked heavily against you.

It's not just that there is usually a price to pay. It's that it betrays such a reckless lack of judgment about protecting the privacy of your children that voters might wonder just how precarious your judgment is on other, less weighty issues; such as free trade, say, or climate change.

Already, Barack Obama is nursing second thoughts about having let his two young daughters be interviewed on the Access Hollywood channel. “I think we got carried away,” he said. “I don't think it's healthy and it's something we'll be avoiding in the future.”

Depending on how big a cynic you are, that sounds either like eating your cake and having it, or like a gambler who lost at roulette begging for his money back. Either way, Mr Obama sounds like a man who has made a very poor call. In US presidential politics, the rule, rightly, has been that children should be seen but not heard.

David Cameron, too, may regret having broadcast his family life to the public. It will be hard for him now to say his children are off limits. Cherie Blair demanded privacy for her family when Tony Blair was Prime Minister, but then blew it by using them as literary loose change in her book, Speaking for Myself, not only breaking her silence on her son's MMR jab, but revealing he was conceived as a result of her having not taken her “contraceptive equipment” to Balmoral.

Politicians should stick to being filmed kissing other people's children, not their own.