“How then is it true that baptism washes away sin, unites us to Christ, and secures salvation? The answer again is, that this is true of baptism in the same sense that it is true of the word. God is pleased to connect the benefits of redemption with the believing reception of the truth. And he is pleased to connect these same benefits with the believing reception of baptism. That is, as the Spirit works with and by the truth, so he works with and by baptism, in communicating the blessings of the covenant of grace. Therefore, as we are said to be saved by the word, with equal propriety we are said to be saved by baptism.” (Commentary on Ephesians)
All of this is well and good, as long as this allows us to say the same thing of infinks as it does adults. The same thing must be true of an infant after baptism as well as an adult, else there is more than one baptism.