How do I explain to a non Catholic?
The core concept of limbo is the idea of being excluded from the beatific vision of God. The word limbo comes from the Latin word limbus which means a border, a hem, or fringe around the edge of a garment. In Catholic theology the word Limbo has two meanings: 1) The Limbo of the Fathers (limbus patrum). After his crucifixion, Christ in his human soul united to his divine person went down to the realm of the dead to release the dead. He opened heaven’s gates for the just who had gone before him (*Catechism of the Catholic Church * no. 631-637). Here are a couple scripture references for limbo of the Fathers: Acts 2:24, 2:31, 1 Peter 3:19-20. 2) Limbo of the Children *Limbus Infantium *. This is understood as “ the permanent place or state of those unbaptized children and others who, dying without grievous personal sin, are excluded from the beatific vision on account of original sin alone (the “limbus infantium” or “puerorum”)” (Catholic Encyclopedia, Limbo). This is not hell, but a place or state of perfect natural happiness. It must be noted that limbo of the children is strictly theological speculation. It has never been an official teaching of the Church.
Concerning those chldren who die without baptism, the *Catechism of the Catholic Church * (no. 1261) says that “the Church can only entrust them to the mercy of God, as she does in her 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. All the more urgent is the Church’s call not to prevent little children coming to Christ through the gift of holy Baptism.”
For a longer discussion of this topic, I recommend the following: