Faith is not a conscious decision of the will. A recent WELS Q & A post on faith features a truly beautiful response. God is so much more powerful and able to create faith in a person than your ability to make a “decision” to follow Christ. God can create that faith through the proclamation of His Word and through baptism. This post also touches on a difficult subject of the faith of an unborn baby. Through this discussion, some beautiful scriptural truths are covered.
Q: “Can a fetus have faith in the womb. I heard that without Baptism a baby/fetus wouldn't be able to have faith because it is too young to understand about Jesus.”
A: Your question deals with a number of issues. The first would be the matter of faith. What is it? Faith is not a conscious decision of the will. Saving faith is something that takes what God offers, in this case, the forgiveness of sins through Jesus Christ. Strictly speaking, it is not something inside of us but something that reaches out and takes what is outside of us--the gospel. We know that infants can have faith because the Bible tells us they can. In Matthew 18:6 Jesus speaks about "these little ones who believe in me." This term would not only include young children and toddlers but also infants as Luke 18:15,16 would reveal.
You also ask, "Can a fetus have faith." We know that this is possible from the example of John the Baptist (Luke 1:44). However, John was an exceptional situation. He was set apart as the one who would announce the Savior's birth. To say that God always works faith in the unborn in this manner would be drawing more than we can from this account. The difficult situation about the unborn is that God has not given us a clear means of grace for them. Baptism is for those who are born. The Lord's Supper is for those who can examine themselves. And the Word of God is preached to those who can comprehend a language. We want to be careful that we don't turn God's Word into a magical means that can work faith in those who do not comprehend a language. The spiritual life of the unborn and the eternal fate of those who die before birth is not addressed in Scripture. Since God remains silent on the issue, we need to do the same.