Tony Abbott's apology came two weeks after Ms Gillard, Australia's first woman prime minister, branded him a misogynist in an extraordinary attack in a speech to Parliament.
Ms Gillard took offense on Tuesday when Mr Abbott attacked the government's announcement that it was reducing the amount of public money parents receive for every newborn.
Parents are currently paid 5,000 Australian dollars for each baby. But from mid-2013, each second and subsequent baby will earn parents only AD 3,000, with government officials explaining that such families could reuse items such as cribs and strollers.
Mr Abbott argued that parents sometimes needed to buy a second crib or a larger stroller that could carry two children.
"I think if the government was a bit more experienced in this area, they wouldn't come out with glib lines like that," Mr Abbott told Seven Network television.
The incident has reminded some of a furor created five years ago by Sen Bill Heffernan, a colleague in Mr Abbott's conservative Liberal Party, who said Ms Gillard, now aged 51, did not deserve a leadership role because she had decided not to have children.
Mr Heffernan described Gillard as "deliberately barren," and argued that without children, Ms Gillard lacked the community understanding required by a leader.
Mr Heffernan later apologised for his "completely inappropriate and insensitive remarks," which were condemned by his political allies as well as opponents.
Ms Gillard on Tuesday called on Mr Abbott to explain his remark. "On families and pressures with children, the government is certainly working with Australian families and we understand many families are struggling to make ends meet," she told Australian Broadcasting Corp radio.
Trade Minister Craig Emerson accused Mr Abbott of "making inferences" against Ms Gillard. All 22 Cabinet ministers have children except for Gillard and Foreign Minister Bob Carr.
Defense Minister Stephen Smith said, "Blind Freddy could have told you the way in which that comment would have been interpreted," adding that Mr Abbott's judgment was under a cloud.
Mr Abbott denied that his remark was aimed at Ms Gillard, but offered an apology.