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Opening his first White House Easter Egg Roll, President Donald Trump extolled the strength of America as thousands of kids, and some adults, reveled in the time-honored tradition of rolling hard-boiled eggs across the manicured lawn in his back yard.

"This is the 139th Easter Egg Roll. Think of it, 139," Trump said Monday, welcoming families to the annual event, which was dampened by intermittent rain. "And we will be stronger and bigger and better as a nation than ever before. We're right on track," he said, speaking of the nation's strength under fewer than 100 days of his leadership.

Trump's wife, Melania, and their son, Barron, 11, and the Easter Bunny joined him on a balcony overlooking the expansive lawn before they went downstairs to join some of the 21,000 people who were expected to attend what is the biggest social event every year at the White House.

Daphne Rank, from Dillsburg, Penn., participates in an Easter egg roll race during the 139th White House Easter Egg Roll. Saul Loeb / AFP - Getty Images

Before joining the festivities with his family, Trump thanked his wife for "working on this for a long time to make it perfect."

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There was, however, some speculation about whether the Trumps would be able to pull off a successful "egg-stravaganza." Planning seemed to get off to a late start, with the Trumps taking longer than in previous years to announce Monday's date.

President Donald Trump and first lady Melania Trump welcome guests to the White House. Win McNamee / Getty Images

Both Trump and the first lady have been slow to fill White House jobs, and at least one regular egg roll vendor took to Twitter, the president's favorite social medium, to remind the White House that a deadline for ordering the wooden eggs that are given out as souvenirs was approaching.

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But the egg rolling event, which dates to 1878, wouldn't be made to disappear. It was just made smaller, down from the 35,000 people who got tickets last year, but retaining such activities as a reading nook, an area to send messages to U.S. troops and an entertainment stage.

"As we renew this tradition, thank you for joining us," the first lady said.

Moments later, Trump blew a whistle three times, each time sending groups of youngsters scurrying to deftly use a wooden spoon to maneuver their dyed egg several yards across the finish line. He, the first lady and Barron also joined kids at a table to color cards to send to U.S. service members.

U.S. President Donald Trump and his son Donald Trump, Jr., watch children roll Easter Eggs at 139th annual White House Easter Egg Roll on the South Lawn of the White House in Washington, U.S., April 17, 2017. Joshua Roberts / Reuters

Trump's older sons, Don Jr. and Eric, and their wives, and daughter Tiffany also attended.

Seven-year-old Johnny Wilmer of Arlington, Virginia, said his egg-rolling effort ended with a second-place finish. It was his first Easter egg roll, and he said while he and his father, Jack, waited for Trump to appear that the experience had been "great."

Over at the reading area, Mrs. Trump read "Party Animals," a story about celebrating differences written by television personality Kathie Lee Gifford.

Costumed characters roaming the grounds included Elmo from "Sesame Street," Dr. Seuss' Cat in the Hat, Teenage Mutant Ninja Turtles and some of the Racing Presidents, who are mascots for the Washington Nationals of Major League Baseball.