SIXTY pounds is a lot to gain when you’re pregnant, but Kate Hudson savored each ounce.

“I always knew I’d be an ice-cream junkie, and I was – Haagen-Dazs Swiss Vanilla Almond,” recalls Hudson, whose son, Ryder Russell Robinson, weighed a whopping 8 pounds, 11ounces, when he was delivered on Jan. 7, in L.A.

And Ryder could have been even bigger.

Hudson’s doctors worried that he might swell to a precariously plump 11 pounds if she waited until term, so they performed a cesarean section and brought him out two weeks early.

Not that Hudson was concerned about the complicated procedure or the beach ball she had to lose afterwards.

“Everyone around me seemed worried about it,” she recalls, “but I thought it was fun to get really big.”

Very little flusters this naturally slim and carefree 25-year-old child of Hollywood, who grew up around movie sets and nabbed an Oscar nomination for her first major role, in 2000’s “Almost Famous.”

“She’s a natural,” says Garry Marshall, who directed Hudson in her new movie, “Raising Helen,” a comedy-drama about a footloose New York fashionista who takes responsibility for her two nieces and nephew after her sister dies.

Marshall has known Hudson since was an 8-year-old rugrat, running around on the set of his 1987 movie “Overboard,” which starred her famous mother and her mother’s longtime boyfriend, Goldie Hawn and Kurt Russell.

“Kate used to sit on my knee and yell, ‘Action!'” Marshall recalls. “And I have a picture of her clicking the sticks together to start a scene.”

It’s something that Ryder will be doing soon.

Hudson and her husband of three years, 37-year-old Black Crowes lead singer Chris Robinson, want to have “millions of babies,” she says – and they’ll all grow up around movies and rock ‘n’ roll.

The couple bought their first house together in L.A. last fall, but right now, the family is in New Orleans, where Hudson is shooting the mystery “Skeleton Key” with Peter Sarsgaard.

Last year, while Ryder was in the womb, Hudson lived on the tour bus with Robinson – and for a while, with another daughter of showbiz royalty, Liv Tyler, whose husband’s band, Spacehog, was opening for Robinson.

Hudson and Robinson chose the baby’s name because he’d always start kicking and dancing when daddy launched into an original tune called “Ride” or his cover of the traditional blues “I Know You Rider.”

Now Ryder gets lots of private concerts at home.

Hudson has been playing piano since she was small, and whenever she’s around one, she usually sits down to belt out an old rock tune – maybe by the Rolling Stones or Grateful Dead – or even one she’s written herself.

“She sings like a rock ‘n’ roll angel, man,” says John Corbett, Hudson’s “Raising Helen” co-star.

Hudson is more modest about her talents.

“It’s a hobby,” she says. But she does work hard at it – “I’m writing lyrics all the time,” she says – and she and Robinson plan to go into the recording studio this summer to produce a CD of Ryder’s favorite songs with backing vocals from Hawn, Russell and Robinson’s parents.

But don’t hold your breath to hear the CD. It’s just for Ryder and his family, and Hudson doesn’t have any plans to record songs for public consumption – at least until she’s had some more time to build up her chops.

“If the day ever comes that I put a record out,” she says, “I will have put a lot of work into it.”

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HOW SHE LOST HER BABY FAT

AFTER Ryder was born in January, Hudson had just three months to lose 60 pounds before she was due on the set of “Skeleton Key,” the mystery she’s currently shooting in New Orleans.

So the movie producers hooked her up with an L.A. trainer and nutritionist, who put Hudson on a hard-core, three-hours-a-day exercise regimen of cardio, weights and yoga.

“It was so intense,” Hudson recalls. “There were times I was so exhausted that I’d just start crying.”

And the pounds slipped off: By the May 1 premiere of “Raising Helen,” she was back to her skinny, “Almost Famous” form.

But she’s not a complete health nut – Hudson has gone back to her cigarette habit.

“It was easy to quit smoking while I was pregnant,” she says. “But I started when I went back to work, because everything got more stressful.”