As their father adjusts to his new role as U.S. president, Sasha and Malia Obama will be making a transition of their own as they move into the White House.

Doug Wead, author of "All The Presidents' Children," has interviewed 19 of the living presidential children.

"They all look back with fondness on the White House years," Wead told CTV's Canada AM on Wednesday.

He said one child described it as "Christmas 24/7."

"The White House is the best part of it, movies before they're even premiered, every gadget and toy comes over the transom," he said.

Still, for seven-year-old Sasha and 10-year-old Malia, Wead said there's no such thing as "normal" anymore.

"Everything they say and do is currency, it has value," he said.

"...They'll be remembered for the rest of their life for what they say or do during these four or eight years."

Wead said the girls will also face challenges in defining their own identities.

"The problem for the presidential children is carving a separate identity from their father and that happens to every one of them regardless of their age during those brief White House years," he said.

To help them with their transition, the daughters of former U.S. president George Bush, Barbara and Jenna, wrote an open letter to the Obama girls.

The girls should "go to anything and everything you possibly can," the 27-year-old twins said.

"Just go," they wrote in a letter published Tuesday in the Wall Street Journal. "Four years goes by so fast, so absorb it all, enjoy it all!"

They also told the girls to:

  • Surround themselves with loyal friends.
  • Trick-or-treat down the plane aisle if you're travelling on Halloween.
  • Cherish your pets "because sometimes you'll need the quiet comfort that only animals can provide."
  • And this: "Slide down the banister of the solarium, go to T-ball games, have swimming parties, and play sardines on the White House lawn. Have fun and enjoy your childhood in such a magical place to live and play."

Their letter concluded with a reminder for the girls to always remember who their father really is outside of the public spotlight.

"Many people will think they know him, but they have no idea how he felt the day you were born, the pride he felt on your first day of school, or how much you both love being his daughters. So here is our most important piece of advice: remember who your dad really is."

Wead said the letter offered good advice for the girls.

"There is the public image and sometimes the child feels like they have to defend that person, who is separate from their own father," he said.

"Every cruel joke, every negative, they'll feel deeply in their heart even at their ages right now."

With files from The Associated Press