Baptism
Acts 2:38-39
Do penance, and be baptized every one of you in the name of Jesus Christ, for the remission of your sins: and you shall receive the gift of the Holy Ghost. For the promise is to you, and to your children.
Context of the passage
Peter's Pentecost sermon calls the crowd in Jerusalem to repentance and baptism as the response to the coming of the Holy Spirit.
Catholic reading
Peter directly links baptism to 'the remission of sins' and extends the promise 'to your children,' supporting both baptismal regeneration and the legitimacy of infant baptism as inheritors of the covenant promise.
Common objection
'For the remission of sins' means baptism follows and symbolizes a forgiveness already granted through repentance and faith, not the instrumental cause of it, and children here just means future generations who repent and believe.
Response
The grammar places both 'repent' and 'be baptized' as jointly necessary for 'the remission of sins,' and the household baptisms recorded throughout Acts (e.g. Acts 16:15,33) without recorded individual professions of faith by every member reflect the early Church's practice consistent with including infants.