The practice of “believer’s baptism” comes about because this is the pattern seen in the Bible as a response to accepting Jesus as Saviour and Lord. The apostle Peter called on people in Jerusalem to “repent and be baptised”, and this pattern of baptism following repentence is repeated in many other places in the New Testament. The Baptist churches follow this practice by choosing not to baptise infants who cannot decide to follow Jesus for themselves; instead, baptism is offered to those who are old enough to have considered the claims of Christ and accepted them. The form of baptism used is by immersion; this again reflects the New Testament biblical practice, and is rich in symbolic meaning about being “born again”.
The fact that Baptists don’t christen children is not to devalue them; we give thanks for every child born in the congregation and dedicate the child, the parents and the church to the task of teaching them what we believe; but we recognise that it is the individual’s choice to accept the Christian faith, not something that is given to them by a religious ceremony.