It is interesting to view the debate in Christian circles between padeo-baptists (infant baptism) and those affirming believer-baptism. On the one hand infant baptists refer to church history (not including the earliest part of church history) as evidence for this practice while believers baptist refer to the non-inclusion of children being baptized as a evidence for believers baptism. I would point you to one key verse initially to look at. It is not my interest to persuade you in any direction on your belief here but mainly to offer a suggestion for you to ponder.
The great commission passage in Matthew 28:19-20 says:
"Therefore go and make disciples of all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Spirit, and teaching them to obey everything I have commanded you..."
What is interesting is that Jesus command was not to make converts, nor was his command to make seekers, his command was to make disciples. The very word presupposes a person who is a student of the teacher. If you are making a disciple then it is most likely this person is a believer. It would seem from this passage that believers are the focus of this baptism and not that the act saves but that it follows from a person devoted to the teaching of the teacher. In this case the person would have to buy in or believe in the teacher in order to follow his command to be baptized. Here is the example then I think of how baptism should be administered, to a person who has come to believe, trust and have faith in the Savior because the disciples were taking the message and "all that I (Jesus) had commanded" to these who became their disciples linking them to Jesus. So faith precedes baptism, and if a person is a disciple then they have the ability to know and understand the message which seems to indicate that infants and the mentally disabled for that matter are excluded here because they lack the mental development to understand the message.
Again it is not my aim to change your mind on your view I only want to lay out an option and ask that you consider this text when you think about how you view baptism. If this provides clarity then I would have done my part.