We should baptize people of any age upon a credible profession of faith. That means there is an openness we should have to even very young believers. And that means there is a binding upon the church’s conscience to make sure that every believer is indeed baptized. Three passages should help us see that:
Romans 6.3-4: “Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? We were buried with him therefore into death in order that, just as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life.” Paul expects we can appeal to any believer’s baptism to help motivate them in repentance. The fact that every believer can remember their baptism is an argument for believer’s-only-baptism; but the fact that every believer should have a baptism to remember is an argument for baptizing every believer, so help us God.
Galatians 3.27: “For as many of you as were baptized into Christ have put on Christ.” This again is an encouragement to all believers about what their baptism meant. Separating a child’s baptism too far from their initial faith in Christ (putting on of Christ) really takes a lot of punch out of this passage.
1 Peter 3.20-21: “…while the ark was being prepared…Baptism, which corresponds to this, now saves you, not as a removal of dirt from the body but as an appeal to God for a good conscience, through the resurrection of Jesus Christ.” Just as Noah and his family expressed faith by going in the ark and being ‘saved’ in the ark, those who go down in baptism are ‘saved’ in baptism. Baptism saves by virtue of what it means when you do it–it is the New Covenant initiatory act of faith in the resurrection. Any who believe in the resurrection should express it (and be allowed to express it) in baptism.
If you’re just not sure if your child has faith, I get it. It’s not easy. But make sure that is all you are wrestling with. I have heard “they’re just not ready” a lot over the years. If what you mean by “they’re not ready” is “I don’t think they believe in the resurrection,” fine. Just keep preaching the gospel to them (and calling them to repent). But if you mean anything else, that has got to be one of the worst double standards we can possibly set for our kids.