Candidates' children joining in as campaigns heat up.

Byline: Julie Hinds

DETROIT _ How can you tell the presidential campaign is really heating up? They're unleashing the kid power.

The Bush twins, 22-year-old Jenna and Barbara, are hitting the campaign trail and going public as never before. In a spread for the August issue of Vogue, they pose in glamorous gowns and dish about karaoke parties and soy lattes.

Their opponents in the charm offensive? John Edwards' tots, Emma Claire, 6, and Jack, 4, who have added a juice box jolt of youthful energy to the Kerry ticket with their photo op romps.

The conventional wisdom is that sons and daughters of candidates don't have much impact on elections. They smile and make nice with the public, but they don't change outcomes.

But this year could be different, especially if polls continue to show President George W. Bush and Sen. John Kerry in a tight race, says Doug Wead, author of "All the President's Children."

"In a close campaign, absolutely everything counts, including the children," says Wead. "But children can also hurt as much as they help."

Consider the Ron Reagan flap. His speech at this week's Democratic National Convention about stem-cell research isn't endearing him to the GOP, the party of his late father, …