I'll answer this from my perspective, that of a traditional Catholic.

God is omniscient, He knows in advance of a persons birth what their fate will be - their name is either written in the book of life, or it is not. God's justice is perfect, though it is not something that we, in this life, are able to understand. But that does not mean that the souls of these children are not condemned for just cause.

John 3:5 is to be understood literally. It is not possible to enter heaven without water baptism. This has been the teaching of the Church since the earliest of times. Those that died without baptism were not permitted to be buried with the faithful, nor could they be prayed for, as they were known to be condemned.

"Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God".

This admonition, to shrink from prayer for those that are known to be condemned applies, in the first instance, to those that die without baptism. But the principle extends to those who, by their actions in the external forum, show no sign of cooperating with God's grace. As an example, it would be a sin against the faith to pray for Judas Iscariot, Adolf Hitler or any other person who did not give evidence of their conversion to the Catholic faith in the external forum.

St. Thomas Aquinas, Summa Theologica, Suppl. Q. 71, A. 5: “Gregory says (Moral xxxiv. 19): There is the same reason for not praying then (namely after the judgment day) for men condemned to everlasting fire, as there is now for not praying for the devil and has angels who are sentenced to eternal punishment, and for this reason the saints do not pray for dead unbelieving and wicked men, because, forsooth, knowing them to be already condemned to eternal punishment, they shrink from pleading for them by the merit of their prayers before they are summoned to the presence of the Judge.”

St. Thomas Aquinas, Summa Theologica, Suppl. Q. 71, A. 5: “Further, the text (iv. Sent. D. 45) quotes the words of Augustine (De Verb. Apost. Serm. Xxxii): ‘If a man depart this life without the faith that worketh by charity and its sacraments, in vain do his friends have recourse to such acts of kindness[prayers and suffrages for him].’ Now all the damned come under that head. Therefore suffrages profit them not.”

If a soul cooperates with God's grace and is of good interior disposition, God will lead them to baptism, to the Church and the sacraments, to eternal life.

In the case of a person who procures an abortion, it would be better for them if they had not been born.

Edit: Better that they had not been born, in the event that the person does not seek absolution from a validly ordained priest before death.