One tour insider says the brothers, famous for their hit "MMMBop," are enjoying extra-curricular practices with their equally adorable opening act, Norwegian babe band M2M. "They're key-swapping with the teen girls for late-night hotel trysts," reports our spy, who adds that they've also gotten in a few steamy sessions backstage.

Though she declined to discuss details, "Yes, M2M are dating the Hanson brothers," a spokesperson for M2M's label, Atlantic Records, confirms.

Hanson's manager, Christopher Sabec, was less forthcoming. "I don't have any comment on that," he told Page Six. "M2M is their opening act, they're friends... Beyond that, you'd have to ask them."

Later he called back to add, "The tour's been a great experience for everyone... I try to let them have as much privacy as possible, so I don't confirm or deny reports on their personal lives."

The songsters have mainly been shacking up at Hiltons during the tour, which started in Washington on Sept. 14 and wrapped up yesterday in Kansas City.

The Hanson brothers are Isaac, 19, the guitar-playing, "smart, geeky" oldest brother; middle brother Taylor, 17, on keyboards, who's "intelligent but freaky" and the best-looking one; and Zach, 14, the drummer, who's "level-headed."

M2M's Marit Larsen, 17, who plays guitar and Marion Raven, 16, on piano, are known as the "Norwegian Hanson" for their perky musical stylings and hits like "Don't Say You Love Me" from their "Shades of Purple" album.

Of course, since there are three Hansons and only two M2Ms, the numbers don't quite add up. But it's not an orgy. Our source says Taylor isn't joining in the fun and games. Marion and Zach have paired up, as have Marit and Isaac.  Page Six Staff