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ISAAC & NIKKI
Ages: He's 26, she's 23
Married for: Nine months
Children: Everett, 3 months
Everett "makes so many funny faces," says Nikki. Celeb impersonations too. "He's got a little Elvis lip curl going on!"

TAYLOR & NATALIE
Ages: He's 24, she's 23
Married for: Five years
Children: Ezra, 4, River, 10 months, Penelope, 2
"Penelope and Ezra like to sing," says Natalie. "They're working on 'Row, Row, Row Your Boat.' In a round!"

ZAC & KATE
Ages: He's 21, she's 23
Married for: One year
Do three nephews and a niece give Zac baby fever? "I have the cold, not the full fever yet!" he jokes. Says Kate: "We'll wait a while."

Zac Hanson knows what you're thinking. "It's a crazy thing to think that I am 21," says the youngest member of Hanson, the band of three fresh-faced brothers that shot to fame in 1997 with the impossibly infectious hit "MMMBop." Crazier still: All three are married, and Isaac, 26, and Taylor, 24, have kids of their own. Through puberty, weddings and diaper changes, the trio continued making music, and on July 24, they'll release their eighth album, The Walk, partly recorded in Africa. (The single "Great Divide," features children from Mozambique and South Africa; all Hanson's proceeds from its iTunes sales go to HIVSA, an AIDS research center in Africa.) And the entire clan—all 10 of them—will squeeze into a single tour bus this summer. How, exactly? "We want to know too," jokes Isaac. Taylor imagines the scene this way: "Somebody's up front doing e-mails, somebody's in the back trying to wrangle a 4-year-old who's throwing Legos." Zac chimes in: "And Cheetos." Before the madness begins, the Hansons gathered in their hometown of Tulsa and caught up with PEOPLE.

See video of the Hansons in their hometown. Go to PEOPLE.com/hansonvideo