Does God tell us how to become His child?
Can we be sure we are?
The answer is yes!, according to the Bible. The secret is to not listen to the world as too many different ideas are being taught. There are 11 examples in the New Testament that show what people did.
The first example is in Acts chapter 2, where Peter preached the first sermon to the Jews who had killed Jesus. Thousands were there. They came from all over for the Passover meal and Pentecost, and 3,000 believed Peter, so belief is important, and notice Peter didn't have to tell them to believe as they cried, "What shall we do?" Belief is the starting point, then Peter told them to "repent and let everyone of you be baptized in the name of Jesus Christ for the remission of sins."
If I tell you to go to the IGA for a quart of milk, does that mean you already have that quart of milk? Thus baptism is the final step that puts one into Christ, Galatians 3:27, and then one's sins are forgiven. The 7th example I want you to notice is Paul and Silas and the jailor who was guarding them. The Lord caused the foundations of the prison to shake, and all the doors were opened and the chains loosed. The jailor was upset as his life would be taken if the prisoners escaped. The jailor asked, "What must I do to be saved?" Paul told him to believe on the Lord Jesus and he would be saved, he and his household. Notice then they spoke the word of the Lord to him and to all who were in his house. I would have loved to have heard that sermon, wouldn't you? To show the jailor repented, he washed their strips, then notice what happened in verse 33. Immediately he, the jailor and all his family, were baptized! Why baptize at midnight? Because that is the final step that puts one into Christ, His body, the church. Then they went on enjoying what all had happened, as the jailor brought them to his house and fed them.
Please read Acts 16 and find out why Paul and Silas were beaten and put in jail and how they didn't run away and were released by the magistrates.
This is just 2 of the 11 examples, and in the 11th one, the Romans believed, repented, confessed, and were baptized and made free from sin, Romans 6:17, 18. Confession is important as some of the rulers in the synagogue believed but were afraid to confess Christ lest they be put out of the synagogue. Thus, to become a child of God, just a Christian, one must believe, repent, confess that Jesus is the Christ, and be baptized. Jesus said it more simply in Mark 16:16, and finally, "Be thou faithful unto death," Revelation 2:10. If you become unfaithful, you will be lost.
Notice, no infants were baptized as one must believe first, plus sinners are to be baptized. Are babies sinners? What is sin?