Organizers of the "Say Nope to the Pope" protest said on Facebook they hoped to show solidarity to abuse victims and "show the Church they don't have the control they used to".
On the eve of Francis' arrival in Dublin, Boston Cardinal Sean O'Malley - the pope's top abuse counselor - said protecting children and vulnerable adults was now the single most crucial issue facing the church.
The pope wrote a letter to the world's 1.3 billion Catholics vowing to prevent future "atrocities" but conceding no efforts "to fix the harm done will ever be sufficient".
"I can not fail to acknowledge the grave scandal caused in Ireland by the abuse of young people by members of the Church charged with responsibility for their protection and education", Francis said.
Pope Francis says he shares the outrage over the failures of church authorities to punish the "repugnant crimes" of priests who raped and molested children, seeking to respond to a global Catholic outcry over the abuse scandal at the start of his visit to Ireland.
A spokesman said he spent 90 minutes with them.
"In recent weeks, we have all listened to heart-breaking stories from Pennsylvania of brutal crimes perpetrated by people within the Catholic Church, and then obscured to protect the institution at the expense of innocent victims", Varadkar said.
Varadkar welcomed the Pope to Ireland on behalf of the Irish people and began by speaking about the history of the Catholic church in Ireland and the part the church played in Ireland's education system and the foundation of the state.
The Pope has arrived in Ireland for a historic two-day visit which has been dogged by the controversy over sexual abuse by the clergy.
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His visit, the first by a Pope since John Paul II's in 1979, is expected to attract hundreds of thousands of Catholics to a series of events in Dublin and Knock.
A Derry MEP will travel to Dublin this weekend to attend a reception with Pope Francis in Dublin Castle during his visit to Ireland, it has been revealed.
"At times in the past we have failed", he said.
"Magdalene Laundries, Mother and Baby Homes, industrial schools, illegal adoptions and clerical child abuse are stains on our State, our society and also the Catholic Church".
The Vatican said the Pope's meeting with sex-abuse survivors would not be announced in advance, and that it would be up to victims if they wanted to speak afterwards.
Francis also mentioned the past remarks of his predecessor, Pope Benedict XVI, who in a 2010 pastoral letter of apology to Irish Catholics "spared no words in recognizing both the gravity of the situation and in demanding that "truly evangelical, just and effective" measures be taken in response to this betrayal of trust".
Still, pictures of the pope were on the front pages of every newspaper on Saturday and there was excitement among some on Dublin's quiet early morning streets as the city centre prepared to go on lockdown amid tight security. More than a million people gathered for the papal Mass in Phoenix Park on that occasion, according to the Irish Times, representing about a third of the country's population at the time. They have overturned a constitutional ban on abortion and legalized divorce, contraception and same-sex marriage.
The Argentinian Pope remains highly popular in Ireland, and tens of thousands of people are expected at Dublin's Croke Park stadium Saturday evening for a concert-style event.