NOTE: Read this article if you dare, Santorum was into it more than you care to admit;http://thenewamerican.com/usnews/politics/10549-santorum-voted-to-subsidize-abortion-planned-parenthood
As far as Romney changing his position, This from a recent article on the subject;
Although pro-life advocates are normally jubilant over abortion advocates converting to the pro-life position, Romneys shift is seen by some pro-life advocates as political in nature occurring around the time he started moving nationally towards a presidential run.
Depending on whether pro-life voters accept the change in position or see it skeptically, Romney has either remained committed to his pro-life views or has used the issue to get in good stead with pro-life voters.
Following the shift, Romney did veto the pro-embryonic research bill but skeptics say the legislature had the votes to override it and ultimately did so. Skeptics also point out that his state-run health care plan provides for taxpayer funded abortions, but those who say Romney is now genuinely pro-life point out that a state Supreme Court decision forced their inclusion over anyones objections.
Romney spoke to pro-life advocates over the weekend at the Faith and Freedom Conference in Washington, D.C, and told the values voters in attendance that, Were united in our belief in the sanctity of human life. The question will be whether voters in places like Iowa and South Carolina believe him.