My thoughts and Scripture to support:
I, personally, do not agree with this doctrine of the "age of accountability", because it simply is not found in Scripture. However, what is in Scripture is the statement from Paul in his epistle to the Romans: " For all have sinned and fall short of the glory of God" (3:23). Now this verse is quoted quite frequently in our circles, but I would say that it certainly is still of good use. This verse tells us that there are none who are considered righteous or justified in God's sight. This takes us to the concept of original sin. This is a widely accepted doctrine among Christians. From birth, we are born into Sin. The moment we are conceived, we are brought into this world as a fallen creature, incapable of justification before God. If you agree with that statement, then we have to face the fact that there isn't an "age of accountability" because we are set apart from God at the start. So, I venture to say that infants do not "get a pass." They/we are sinful from our beginning.
This brings me to the next topic, infant Baptism. This is something I wrestled with quite heavily a few years ago. I was raised in the Baptist church. As is common with Baptist theology and practice, Baptism is viewed as nothing more than a profession of faith. This is an outward act, or show, reflecting an inner change. This really was a difficult idea for me to abandon as it was what I had been taught, and believed, for many years. After doing much study in the area, my views changed. I believe that the Old and New testaments (covenants) tie together quite harmoniously. In the Old Testament, in God's covenant with Abraham, there was no practice of Baptism. However, we see the practice of circumcision instead. This was for both adults and infants. It was instructed that every child was to be circumcised on the 8th day after birth. This practice was done to show that the man, or child, belonged to God. It was an inclusion into the covenant.
Now in the NT, Paul makes it very clear that it is no longer circumcision, but Baptism. Christ himself says in Mark 16:16 "Whoever believes and is baptized will be saved." And Peter states in Acts 2:38, "Peter replied, "Repent and be baptized, every one of you, in the name of Jesus Christ for the forgiveness of your sins. And you will receive the gift of the Holy Spirit." This verse explicitly states that Baptism works forgiveness of sins. These men also spoke of this Sacrament being set up for children as well. It is for everyone.
Here is a great article on the subject.
http://www.opc.org/new_horizons/NH00/0007c.html
When I (and many others) read these verses, I can no longer see baptism as a "show of faith." If this were merely a show, it would not be commanded, but suggested. Both verses use very authoritative language.
To summarize, I believe that the Bible teaches that we are all born into Sin. I believe the Scriptures show infant baptism. And I believe that Baptism is God's grace in the form of a sacramental gift to believers and their children.