Megan Fox is only 25, but the brunette bombshell is ready to start a family with husband Brian Austin Green

"I want at least two, probably three (kids)," Fox says in the April issue of Cosmopolitan, where she sizzles on the cover. "I've always been maternal." Fox is already a step-mom to Green's 9-year-old son with his ex, Vanessa Marcil.

The Transformers' star and her hubby tied the knot in June 2010, but Fox acknowledges their marriage has its ups and downs.

"We've had obstacles, and we've overcome them," she says. "I truly feel like he's my soul mate. I don't want to sound corny or cliche, but I do believe we are destined to live this part of our lives together."

Even though the couple started dating in 2004, Fox reveals she was clueless about Green's big claim to fame. "I was too young for Beverly Hills, 90210. But the first time I saw him, I got butterflies. And the first time he casually touched me? There was so much electricity."

The magazine hits newsstands March 6.