Teaching Kids to Pray as Reason to Baptize Them?

Dr. Sean Lucas uses an article from Baptist pastor, John Piper, on teaching kids to pray to reason for infant baptism. He writes:

This is an interesting set of reflections from John Piper. They actually strike me as providing a pretty strong case for applying the sign of the covenant (baptism) to a child.

After all, if you are going to 1) admit that you cannot know when a child is regenerate; and 2) treat the child as though they have covenant responsibilities which arise from belonging to a Christian family (or in Piper's language "treat them as a believer"); then 3) applying the sign of entrance into the covenant community (i.e. baptism), a sign that authenticates (or "seals") God's gospel promises for him and invites him to respond by faith, makes a whole lot of biblical sense.