Here is an excellent mp3 message by Dr. Thomas Schreiner in defense of Credo baptism. Worth checking out, as it's an excellent defense packaged into a 30 minute time frame. Some notes I took from this message:
In the baptist view, believers are clothed with Christ at baptism. Peter's message at Pentecost was "Repent and be baptised". Numerous NT scripture references all cite baptism following belief. In the Presbyterian paedobaptist model, the baptism provides no benefit unless it's followed by later faith. Faith MAY occur later in life, or may never occur at all.
I Cor. 12:13 - All believers are baptised in the body of Christ in one spirit..." All believers drink of the spirit and are equal members at baptism. Have infants received the spirit at baptism? (baptismal regeneration).
Baptism is also described scriptually as a "washing". I Cor. 6:11 - makes it clear that washing of sin and justification take place at the same time, yet justification involves faith. Justification is for those who believe.
"Household baptisms" of scripture (Acts 16) does not support the notion that this included infants. The household is contextually limited to those who could understand and believe. Evidence for this is that the household is described as "rejoicing". This joy implies understanding the significance of what had happened. Those who had rejoiced were those who believed - no compelling evidence that this included infants.
Acts 18 - Belief of the household meaning mental understanding. Maybe children included. Acts 2:39 - Often used in defense of infant baptism. Peter states "The promise is for you and for your children..." A careful reading of this does not include infants. The groups are Peter's listeners, the children, and those far off (the gentiles). It's not all those listeners, but only for those from every group who believe in the Gospel. This is justified by the last clause in the verse, "that is everyone that the Lord has called to himself." How would baptized infants who turn from faith later in life apply to this group?
Baptism as covenental sign (col. 2:12) continuing circumcision. "In him you were circumcised..." The parallel, however, doesn't work for a number of reasons: it lumps the plans of God together. There is one plan of God from scripture, but there is no evidence from scripture that we have one covenant of grace. The Abrahamic covenant is clearly distinguished from the Mosaic covenant. It is also clear that the new covenant and the Abrahamic covenant are not the same. There are elements unique to the Abrahamic covenant. For instance, Ishmael receives the covenental sign of circumcision. There is a genealogical principle to the Abrahamic covenant that does not continue in the new covenant. There is continuity and discontinuity in both covenants. The old covenant was a nation and a church. This is no longer true in the new covenant - the new covenant is composed only of those who believe in Jesus Christ. There is no special chosen nation. Heb. 8-10 make it clear that all members of the new covenant are forgiven of their sin and filled with the Holy Spirit. People from every people group.
The new testament supports a credobaptist position.