I’m newly saved and born again. I have already raised my family, so my children, now all in their twenties, were not raised knowing and understanding what they needed to know to insure their salvation. I am consumed with guilt and worry over that. Would God really cause these good people, my children, to suffer for eternity because they’ve not yet come to understand? That doesn’t seem right to me and I struggle daily with it. Their lack of understanding is my failing, not theirs.
When your children became intellectually mature enough to understand the sin/salvation equation, they became accountable for themselves in God’s eyes and you were relieved of any responsibility for their salvation. The truth be told, most Christians become believers as adults just as you have. Romans 1:18-20 says the creation itself bears witness to God’s existence, and no one can fail to understand this, so somewhere in their heart they already know He’s out there.
Your primary responsibility now is to be an intercessor for them, praying that their hearts will be opened to the gospel while there’s still time. This is the Lord’s will for them since He doesn’t want that any should perish but for all to come to repentance (2 Peter 3:9) but ultimately it’s their choice.