Here is another wonderful difference between the church of Jesus Christ and the Old Testament order. This is not about heaven; it refers to the New Testament church during its time on earth.
Within the church, the people of Christ, we will not be saying to each other know the Lord for we shall know him. We should not have to evangelise within the membership of the church; the New Testament church is about communion with God. That does not mean we do not preach the gospel to outsiders, but if they are converted they come into the church as those who know the Lord. Of course even the best church will have some phoneys, but we try as hard as we can not to allow this.
Those churches which admit members as infants or children, simply because they are the children of believers, do not fully understand this. Such children are usually admitted on the basis that they have some kind of covenant status on account of their parents. Later they may come to exercise faith themselves. But while the children of believers are born into the world with a huge advantage and will be taught Scripture on their parents’ knees, and while God is pleased to call many of the children of his faithful people into the covenant of grace, they must have their own spiritual awakening. Before that they need to be evangelised like anyone else. Yes, Scripture teaches that there is an age below which the children are not yet accountable, but we must teach them as early as we can from God’s word.