Siblings the Band Perry (from left, Reid, Kimberly and Neil) are quickly becoming country stars. (All photos by Marvin Joseph/TWP)

“It was too dark for kids and too childlike for adults,” says Reid Perry, bassist and middle brother.

Even if the Band Perry’s music comes from a similar in-between space, no one would call the group underrated. In less than a year, its popularity has exploded thanks to “If I Die Young,” a stunning ballad that topped the country charts in December, earned a Grammy nomination and is nudging the band’s superb self-titled debut from gold toward platinum. On next Saturday, they’ll sing it when they open for Tim McGraw at Jiffy Lube Live.

And although the Band Perry’s career seems headed up, up, up, its album is full of songs that pull in different directions. The members sing about leaving their home town in the dust while longing for the comforts of home and breaking hearts while pining for true love. Their songs feel young and old, naive and wise — which might explain why so many kids go to see the Band Perry in concert with their parents, grandparents or both.

“We walk a fine edge between the surreal and the romantic,” says Kimberly, 28. She and brothers Reid, 22, and Neil, 21, are taking a dinner break on their palatial tour bus after a performance at the Delaware State Fair, where they preceded “If I Die Young” with a punchy cover of Queen’s “Fat Bottomed Girls.” Their mom, Marie Perry, hands Kimberly a peanut butter sandwich. It’s cut in half, the way that only moms cut peanut butter sandwiches.

“Our cheek muscles are strong,” says Kimberly, smiling, or flexing.

All day, Marie Perry has played stealth stage mom, foofing bangs before the cameras flash and conjuring snacks from thin air. She doesn’t speak to reporters, but you can tell she’s concerned about her kids as they try to pen a hotly anticipated sophomore album in the middle of a tour that won’t bring them home to Greeneville, Tenn., until late November.

On a schedule this grueling, the Perrys’ only reprieve is sleep — which doesn’t always help.“I've even been dreaming about the songs we’re working on,” Kimberly says.

On nights before a rehearsal, Kimberly could never sleep. At 15, she was fronting a rock band of high school buddies called Rain, named after the weather the day the group formed in Mobile, Ala. Neil and Reid — then 8 and 10 — would watch their big sister practice in the living room with awe. Whenever her bandmates left for a glass of water, they’d rush to grab the drumsticks and bass guitar.

The boys eventually started their own group — “the Mobile Music Machine,” Reid says, almost blushing — and would rehearse in the foyer of their pediatrician father’s practice. (These days, papa Perry works in Tennessee while his wife travels with the band. His name is Steve Perry. No, not Steve Perry from Journey.)

In 2005, Reid and Neil were finally tall enough to stand next to their sister onstage without looking ridiculous, so they started performing together. Reid played the bass, and Neil picked up mandolin and accordion. Everybody sang.

“I think we always knew we were gonna do the family band eventually,” Reid says. “We needed a lead singer, and she needed a band.”

They embarked on a radio-sponsored tour of Wal-Marts across the Southeast. “With the panties and the bras,” Kimberly says of the band’s early gigs in Bible belt lingerie departments.

It was there that the trio nurtured a sibling chemistry for vocal harmony that would propel the songs they had written in their parents’ basement in Greeneville, where they moved to in 2002. They’d start recording them after Garth Brooks’s manager, Bob Doyle, discovered the group in 2008. In 2009, the Perrys were signed to Republic Nashville by Scott Borchetta, the man credited for launching the career of Taylor Swift. In summer 2010, “If I Die Young” was all over country radio. This summer, it has crossed over to pop radio.

Since the band’s album was released in October, it has produced other big singles — the jouncy “Hip to My Heart,” the fiery “You Lie” — but “If I Die Young” is the song the trio hears about over and over again, on Twitter, on Facebook, and in the autograph lines that form after every gig. Equal parts sentimental and fatalistic, the song imagines the fallout of a premature death in sepia-toned melodies that have touched listeners who might have lost someone too soon.

“All the stories come out of the faucet,” Neil says of fans’ intense response to the song. “It’s been really cool to be a part of these people’s lives in a very personal way. I think that’s what country music is.”

The lights of the fair are hardly visible from the tinted windows of the Perrys’ tour bus, but they still enjoy being near it. The trio has toured the state fair circuit heavily in previous summers, and various swatches of carnival imagery have seeped into the band’s lyric sheet along the way.

Walk Me Down the Middle” depicts a young romance blooming beneath the glow of a Ferris wheel, and “Lasso” describes love as “a ride on a tilt-a-whirl that sits on top of the world.” They loved going to the fair as kids, and they still like to watch Ryan and Tatum O’Neal in the Peter Bogdanovich flick “Paper Moon.”

“The image of the fair in that movie is always in our heads when we’re writing,” Neil says.

Tonight, movie memories will have to do. They can’t sneak out on to the midway for a funnel cake or ride on the teacups. There’s a sophomore album looming, and the Henningsens — a father-son-daughter songwriting team that the Perrys have a rapport with — have been flown in for a writing session.

The band writes nearly all of its material and says that other songwriters are brought in to keep them on track and pull their tunes into focus.

“We have a lot of ideas swirling around,” Kimberly says.

Then “somebody comes along with a needle and thread and helps us sew up allof these really cool ideas.”

Most of the ideas on the Perrys’ first album formed in Greeneville, where Reid, Neil and Kimberly all still live with their parents. There’s no point in buying apartments or building houses when they were home only 19 days last year, they say.

“The biggest pressures, to me, are the ones that come externally — the pressure of trying to maintain the pace on the road,” Kimberly says. “Some days, you want to go home.”

Marie Perry silently glides up the tour bus stairs carrying three huge bags of cotton candy. Her children laugh, jump up from their seats and start tearing into pillows of pink and blue.