WASHINGTON - Ryan Costello had no idea how fast his life would change.

A Chester County commissioner whose first baby was born last December, Costello didn't know that less than 12 months later, he would have launched and won a campaign for Congress, and that he'd be walking the same halls as national leaders and attending a meeting in the Oval Office.

"My little boy can take eight steps," Costello, 38, said last week. "When the campaign first started, he couldn't even roll over."

Costello is one of four newly chosen members of Congress from the Philadelphia area who have been through a whirlwind transition since winning elections Nov. 4.

A Republican, he leapt into an unexpected opportunity when U.S. Rep. Jim Gerlach (R., Pa.) made a surprise announcement in January that he would not seek reelection.

"It's fascinating how quickly life events can change," Costello said by phone as aides closed up a district campaign office he opened in February.

State Rep. Brendan Boyle, a Philadelphia Democrat, and Tom MacArthur, a South Jersey Republican, are making similar transitions.

Former New Jersey State Sen. Donald Norcross, a Democrat, had to move even faster: after winning a special election, he's already been sworn in, has taken his first big vote, and has landed a plum political post as he, too, learns the ropes in Congress.

Before a recent interview, Norcross looked for a quiet place to talk, stepped into an office marked for House members and media only, then realized he didn't know whom the office belonged to. He quickly stepped back into the Capitol's marbled hall.

Other new members admitted they were still baffled by the byzantine tunnels beneath the Capitol.

"I just follow somebody," Costello joked.

Each of the new congressmen is replacing one who didn't seek reelection. Boyle, Costello, and MacArthur are due to be sworn in Jan. 6.

Last month, they went through an intensive eight-day orientation that included everything from ethics training to advice on setting up a staff and constituent services to choosing an office.

Along the way were moments that drove home the history they are about to become part of.

MacArthur and Costello singled out a meeting in the Oval Office between the new freshman class and President Obama's chief of staff, Denis McDonough. MacArthur, until this year mayor of Randolph (population 25,000) in North Jersey, recalled a dinner for GOP freshmen in Statuary Hall, ringed with marble columns and burgundy drapes with gold fringe. It was once the meeting room of the House of Representatives.

"We were sitting right next to where Abraham Lincoln had his desk in Congress," MacArthur, 54, said. "That was sort of one of those 'pinch yourself' moments."

At a dinner for Democratic newcomers, Boyle told how Vice President Biden "made a beeline" for Boyle's 10-month-old daughter, Abby. When Boyle, 37, posted a photo of them on his Facebook page, 710 people clicked "like."

He also had a 30-minute congratulatory call from former President Bill Clinton - who had campaigned for one of Boyle's primary opponents: Marjorie Margolies, mother-in-law of Clinton's daughter, Chelsea.

Amid the sparks of wonder was also recognition of what lies ahead.

"I was struck over and over with the sense of the opportunity that we have," MacArthur said.

Norcross, 55, had to balance the orientation - running, he said, from 7 a.m. to 10 or 11 at night - with learning issues and voting.

Days after taking office, he was one of 31 House Democrats to cross party lines and vote in favor of a bill to approve the Keystone XL oil pipeline, saying it would create jobs.

If party leaders were angry, they didn't show it. Norcross was one of two freshman representatives named to the House Democrats' Steering and Policy Committee. (His family, of course, travels in elite Democratic circles, thanks to his powerful brother, George E. Norcross III).

"It's an honor to be here, but you don't have time to be excited," Donald Norcross said. "The only thing we need to be focused on is what we were sent here to do."

Overall, 58 new House members have won seats, with three races still undecided. Three of them, including Norcross, had already taken office after winning special elections.

Some, like Utah Republican Mia Love and Florida Democrat Gwen Graham, already are building national profiles. Costello, who played basketball growing up, likened the orientation meetings to the early days of an invite-only basketball camp: "Everyone's sizing each other up."

For Boyle, his time as a state representative in Harrisburg has helped prepare him for Washington.

"It is more similar than dissimilar to what I've already experienced," he said, citing the requirements of setting up a district office, managing a budget, understanding voting procedures, and introducing bills.

His state House and congressional districts both include parts of Montgomery County and Philadelphia. But now he'll be serving 10 times more people.

For now, before the voting begins, the focus is on details: hiring staff, jockeying for committee assignments, preparing offices and constituent services.

He and the others also have had to join the office lottery: a drawing among new members to decide the order in which they choose office space.

MacArthur went 47th - landing on the difficult-to-reach fifth floor of the Cannon House Office Building. He kept a positive spin on it: He at least had first pick on that level. (Boyle called the floor "infamous").

"Some are nicer than others, but they're all full of history and people who have served before," MacArthur said. "The fifth floor was home to Richard Nixon and Lyndon Johnson when they started their House careers."

Boyle hopes to land on the House Education and Transportation Committees but also wants to open a new avenue if he can get on the Foreign Affairs Committee, embracing an area he didn't get to touch in state government.

Costello has interests in veterans, education and the workforce, and transportation.

He'll leave his post governing a patch of Pennsylvania on Dec. 15, soon to tangle with issues such as immigration and U.S.-Iran negotiations. He is eager for a new opportunity, but is also cautious.

"I'm learning that I need to be very careful with my opinions because it's no longer just my opinion as the average citizen," Costello said. "It carries with it a certain added significance because of the position that I hold."

@JonathanTamari