a child who has reached the age of discretion (generally age 7) is considered an adult, no longer an infant, for the purposes of the Sacraments of Initiation (Baptism, Confirmation, First Communion). He will participate in the Children’s Catechumentate, that is RCIA (Rites of Christian Initiation) with his peers, and be received into the Catholic Church during the Easter Vigil through all of these sacraments, and continue with faith formation throughout his school years, and hopefully as an adult as well. He will prepare for his first confession some time after Easter.
He may be in a class with others of his age preparing for first communion, or if there is a large number of children needing baptism, they will all be in one class. There should be at least a year of pre-catechumenate or inquiry, where he is introduced (according to his learning and grade level) to the basics of the salvation story in the bible, the person of Jesus Christ, the basic beliefs and practices of the Catholic Church, and when he is ready, through the Rite of Acceptance, begin the catechumenate not less than one year before the Easter in which he will be received.
consult the parish in which you will be participating and worshipping for referral to the person in charge of this program.
on his behalf, welcome home.
the 4 yr old is considered an infant in this context, would be baptized the next time the parish baptizes infants, usually parents and godparents are required to attend a class first, and then will enroll in religious education classes when he starts school, and celebrate the other sacraments at the normal age for your diocese.