Ms McAleese, a Catholic, accused the Vatican of reversing its position on parental corporal punishment, and questioned whether the pope "has turned the clock back considerably".
In a letter to the Irish Times, she said: "What faith are we to have now in the Holy See's commitment to the Convention on the Rights of the Child?"
"Is the Holy See now doing what it claimed not to be doing a year ago, namely actively and internationally promoting the corporal punishment of children?"
On Thursday Pope Francis said he supported parents who smack their children at his weekly general audience, which was devoted to the role of fathers in the family.
Francis suggested parents show forgiveness but also "correct with firmness" while not discouraging the child.
The Pope said: "One time, I heard a father in a meeting with married couples say 'I sometimes have to smack my children a bit, but never in the face so as to not humiliate them'.
"How beautiful! He knows the sense of dignity! He has to punish them but does it justly and moves on."
The Pope's remarks come after the UN human rights committee sharply criticised the Catholic Church's position on corporal punishment last year, as part of a report monitoring the implementation of the UN treaty on children's rights.
Recommendations by the committee were prompted by reports of widespread physical abuse and the use of corporal punishment in Catholic-run schools and institutions, which it said had reached "endemic levels."
The Vatican responded by saying that it did not promote corporal punishment, and it had no power to enforce any kind of ban in Catholic schools, and was only responsible for protecting children in the Vatican City state.
Under the treaty, corporal punishment, including at the home, is prohibited in as many as 39 countries from Sweden and Germany to South Sudan and Turkmenistan.
The UK is not a signed up member of the treaty, with the Government saying: "the use of physical punishment is a matter for individual parents to decide".
