Information to teach these passages
I would suggest that you first review the passages dealing with circumcision in Genesis and the institution of the practice in Israel. Note the failure to perform this practice following the exodus from Egypt. Then note that circumcision is the sign of the covenant with Israel while baptism is the sign of the covenant in the Church which is why we baptize infants. I'll not detail a great amount of information since you can search for this yourself, but since the Encyclopedia of the Reformed Faith is, I believe, no longer available from Logos, I will quote a bit.
"Reformation teaching on Baptism was less disputatious than on the Eucharist but followed similar lines of thought. In place of the baptismal regeneration of Rome, there was explicit emphasis on the Word, faith, and the Holy Spirit. Within Protestantism there were those who saw Baptism as little more than a badge indicating belief or sign of the covenant. But most Reformed people, including the Church of England, believed that Baptism was a real means of grace with multiple significance: the acknowledgment of sin, of cleansing through Christ, union with Christ, the gift of the Holy Spirit, and Baptism as a sign of covenantal status. As a covenantal sign, it was seen as replacing circumcision (Col. 2:11–12). Because of Christ’s redemption, it has a richer meaning than the OT ordinance. There was debate about the candidates for Baptism and the amount of water that was proper to use. But there was nothing like the acrimony which attended the "sacramentarian controversies" over the Lord’s Supper."
McKim, Donald K. and David F. Wright. Encyclopedia of the Reformed Faith. 1st ed. Louisville, KY; Edinburgh: Westminster/John Knox Press; Saint Andrew Press, 1992.
If you have Schaeffer's complete works, he deals specifically with this passage beginning here <logosres:cwfs;art=sSub2-3~5.3>. Of course, there are commentaries dealing with the passage as well.
