The Bible does not teach the Age of Accountability. Children are sinners as much as anyone. They are sinners from conception and do not receive special treatment from God just because they are babies or children. The depravity, or sinfulness of man is a doctrine which is vital to understanding salvation. Because most of the church today does not understand the doctrine of the sinfulness of man.
People think that man still has the capacity to be good.
They think people are able, in and of themselves, to do works of righteousness before God without the help of God at all. Lost people cannot work righteously before God. Saved people, by the power of the Spirit of God, are able to work righteously only because they have the Spirit dwelling in them. Whenever someone says that they can believe in Christ for salvation on their own, or choose to follow Him on their own before the Spirit of God changes their heart, then they are saying man is good because the Fall of Adam has not totally corrupted them. They are not following the Bible at this point, but rather the teaching of Pelagius.