It’s a privilege to grow up in a Christian environment, and be taught the Word of God as a child. (2Ti 3:15) If that’s been our heritage, we should be grateful, yet not presume we’ve always been a child of God because of this.
We all start out dead to God (Ep 2:1), seeking our own way and will (Tit 3:3), blind in our ignorance, alienated from God’s life (Ep 4:18) and under His wrath. (Ep 2:3) We may not seem as bad as those from more broken backgrounds, but measuring sin as the world does is unwise at best: in our selfishness and pride we’ve all been an abomination to God. (Pr 16:5)
So, God says we must each be born again (Jn 3:7), born anew, each and every one of us; in order to enter Heaven, at some point we must be converted (Mt 18:3), regenerated, made alive. (Ep 2:5).
It isn’t that we must know the exact day and hour we came to Christ, any more than we’d know exactly when we were born physically if no one told us. But the significance of the new birth, requiring that we understand the basics of the gospel and trust God for eternal salvation, and the radical inward transformation that always accompanies this miracle of God (Jn 1:13), suggest we’ll know the general time period, and distinctly remember experiencing assurance of salvation as we began our faith journey. (1Th 1:5)
Thinking we’re Christians simply because our parents were, or because they had us baptized, is to ignore our need for personal salvation and regeneration. There’s no guarantee of heaven in any ritual, or in the faith of others (Ga 6:15): we must each strive to enter the kingdom (Lk 13:24), seeking God until we find Him for ourselves. (He 11:6)
We should each examine ourselves, whether we be in the faith, and prove our salvation (2Co 13:5), laying hold on eternal life (1Ti 6:12), and ensuring the evidences which accompany salvation appear in our own lives. (He 6:9)