Baptism has no saving effect, it is a sign -
of our welcome into the family of God - born of water; John 3
or the baptism of the Holy Spirit giving us new life - born of the Spirit; John 3
of union with Jesus in his death & resurrection; Romans 6
of our recognition of our sinfulness & repentance & need of cleansing from sin by the sprinkled blood of Jesus; Acts 2
a sign of the New Covenant in the blood of Jesus, as circumcision was a Covenant sign given to Abraham for his descendants; Heb. 9 & 12
a sign of the New Covenant in the blood of Jesus, as the Exodus 24 sprinkling with blood was a sign of the Old Covenant; Heb. 9
a sign of the intention of parents to bring their children up in the training and instruction of the Lord, and to instruct them in the significance of their baptism. Eph. 6
As baptists, we would insist that baptism requires repentance & saving faith, therefore at an age of understanding, and also immersion in the name of Father, Son & Holy Spirit.
BUT
We know that the weight of Gospel history is the practice of infant baptism, & vast numbers of faithful believers & Gospel preachers were baptised as infants, usually by sprinkling. They lived as baptised believers as we seek to.
When faithful Christians baptised in infancy seek membership in a baptist church, they should be encouraged to accept baptism as believers, but if they can present a coherent Scriptural defense of paedobaptism as indicated above, they should be welcomed without what should be considered re-baptism.