There aren’t any specific scriptural passages about miscarried children, or even about the fate of infants who die before they are baptized. You may have heard of the hypothesis of “limbo” which developed a few hundred years after the life of Jesus. At that time, theologians were debating what happens to children who die before they have committed any sins but before they have original sin washed away by baptism. If baptism is considered necessary to be saved, it is a theological problem to imagine that without being baptized a tiny infant would go to hell. So the theory of limbo was proposed, suggesting that these children are in a state of “limbo” (related to the words “liminal” or “edges”) rather than in hell or heaven.
This is not an official teaching of the Catholic Church since nothing has ever been defined on the fate of these little ones. Pope Benedict XVI recently proposed other theories around this, essentially weighing what is found in the Catechism of the Catholic Church — Nos. 1260, 1261, 1283 — that we have a right to hope that God will find a way to offer the grace of Christ to infants who have no opportunity for making a personal choice with regard to their salvation.
Many Catholics have expressed greater hope and trust that an all-loving God will indeed welcome such children into heaven.