As Media Matters reports, there is a generally understood rule that journalists do not disclose the location of the children of presidents when they're not with their parents, because their security should not be placed at risk.
The Washington Post's Paul Farhi reported at the time that this is part of a longstanding and informal agreement between successive administrations and the White House Correspondents' Association, and that "traditional news organizations have long abided by such arrangements":
Presidential administrations have long been protective of the first family's minor children, and reporters in Washington have mostly observed the taboo on stories or photographs of them outside official and semi-official events. The ban on such coverage has existed through many administrations by informal agreement with the White House Correspondents' Association, which represents the interests of journalists who cover the president.
But Breitbart's Matt Boyle disregarded such tradition and related security concerns when he posted an "exclusive" report on Breitbart.com detailing where the Obama daughters were vacationing for spring break. Boyle said that the White House declined to comment and that the Secret Service told him they don't "confirm or deny trips for anyone under the agency's protective detail, including Sasha and Malia."
These small considerations are considered trivial to the Breitbots, who are very, very determined that we all become outraged over the very idea that Sasha and Malia might have a spring break like normal children. They resent the fact that the girls do have a security detail, all the while whipping up the outrage that makes it necessary. Funny how that works. I don't recall right (or left) wing media outlets dogging the Bush daughters like that.