A new hypothesis has appeared which would place all infants, baptized or not, in heaven. The Catechism of the Catholic Church gives an ambiguous answer based on the following proposition:
Christ died for all, and since all men are called to one and the same destiny,
which is divine,
we must hold that the Holy Spirit offers to all the possibility of being made partakers,
in a way known to God, of the Paschal mystery." (Cat.of Cath. Church #1260) The conclusion reached below is based on hope as follows:
"As regards children who have died without Baptism, the Church can only entrust them to the mercy of God, as it does at funeral rites for them. Indeed the great mercy of God who desires that all men should be saved, and Jesus tenderness toward children which caused him to say: 'Let the children come to me, do not hinder them, allow us to hope that there is a way of salvation for children who have died without baptism. (Cath. of Cath. Church # 1261)
Besides Baptism of water, Baptism of Blood (e.g. Infants who died for Christ as when Herod killed the children of Bethlehem hoping to kill Christ) had always been seen as a way of salvation for unbaptized children.
More than one theory has tried to explain the extra-sacramental salvation of children such as prayer and desire of the parents, the prayers and desire of the Church, the suffering endured by a child in dying and the attainment of the use of reason at the moment of death so that a child may decide for or against God. All of these are possibilities but they cannot be proven. God certainly is not bound by the sacrament of Baptism but the Church knows of no other sure way of salvation. (Ibid., #1257)
I do not believe that the Church will ever be able to say that all infants are in Heaven. The question for Christians is: Is it more reasonable to believe in Limbo which is solidly grounded in Tradition or the proposition of uncertainty based on the salvific will of God?