Moore, 42, tells the upcoming issue of Harper's Bazaar that the "next phase" of her relationship with Kutcher, 27, will be "to expand our family," Zap2it.com reported Monday.
Moore has three daughters -- Rumor, Scout and Tallulah -- with ex-husband Bruce Willis.
Her May-December relationship with the star of "That 70s Show" was met with skepticism at first, but is still going strong after two years, Zap2it.com noted.
In the interview, Moore describes Kutcher as her "soul mate." But when asked if marriage is in the future, Moore said they do not "need something formal" to solidify what they have.
She said their favorite activities include "sharing a bath with one another and watching 'Court TV.' Snuggling up naked."