Regeneration is necessary because all descendants of Adam and Eve have inherited their sin and are morally unable to do what is good. Paul wrote to the Ephesians that people are by nature dead in trespasses and sins. In this state, they are without God and without hope in the world. Not in response to their merit, but freely and in love, God speaks the word that raises the dead.
(because all have sinned, then all the more reason for Jesus to die for all.)
TROUGH BAPTISM, Baptism imparts regeneration and ANYONE can receieve baptism, especially infants. Because Jesus said NO ONE comes to the Father but by me, so that includes infants and children as well, and as in the above quote, ALL have sinned, ALL are born into sin, this would mean that infants have the need to be regenerated too.
John 3:5
Nicodemus said to him, "How can a person once grown old be born again? Surely he cannot reenter his mother's womb and be born again, can he?"
5
Jesus answered, "Amen, amen, I say to you, NO ONE can enter the kingdom of God without being born of water and Spirit
I would seriously think NO ONE includes infants and children.
CCC:
An indelible spiritual mark . . .
1272 Incorporated into Christ by Baptism, the person baptized is configured to Christ. Baptism seals the Christian with the indelible spiritual mark (character) of his belonging to Christ. No sin can erase this mark, even if sin prevents Baptism from bearing the fruits of salvation.[82] Given once for all, Baptism cannot be repeated.
1273 Incorporated into the Church by Baptism, the faithful have received the sacramental character that consecrates them for Christian religious worship.[83] The baptismal seal enables and commits Christians to serve God by a vital participation in the holy liturgy of the Church and to exercise their baptismal priesthood by the witness of holy lives and practical charity.[84]
1274 The Holy Spirit has marked us with the seal of the Lord ("Dominicus character") "for the day of redemption."[85] "Baptism indeed is the seal of eternal life."[86] The faithful Christian who has "kept the seal" until the end, remaining faithful to the demands of his Baptism, will be able to depart this life "marked with the sign of faith,"[87] with his baptismal faith, in expectation of the blessed vision of God - the consummation of faith - and in the hope of resurrection.