Baptism is a seal upon a believers and infants life; it is a powerful sign of God's covenant, and a powerful seal of God's promises. Reminding us of the vows the Lord has made unto us and we unto him.
The case for an infant to be baptised is simply for them to never remember a time they didn't know God - we are all united as one in baptism which is through Christ (see Gal 3:26-28; col 2:8-14).