We all want, desperately, for our children to follow Christ. When those children as adults are far away from Christ, we often despair. Be sure of this, it is never too late.
It is much harder to bring someone into the faith or back into the faith when they are adults but
our God is a worker of miracles.
Often a flaw in our efforts to evangelize adults that are close to us is to think that we can reason them into faith. "If I can just find the right argument they will get it."
Other broken methods are trying to guilt them or cajole them or scare them into it.
Many others think that if we just tell them to come to church enough times they will wear down and one day come. Give that up.
Though Paul had a sudden experience of transformation, this is not typical. Usually coming to faith is a process.
The first step in that process is Affiliation.
Affiliation is the stage in formation when people are warming up to the church and Christ. It is just like meeting someone - it is meeting someone, actually. If you are introducing two people that you want to become friends, you make the first meeting light and pleasant in a nice atmosphere. You want them to warm up to each other. This is the first step in bringing adults to faith. If you have been pursuing your child, it will take a while for them to get over that history so be patient. They need time to unlearn what you have been giving them. Drop every other strategy. Quit talking about Christ. Quit trying to win them. Quit telling them that they are not a Christian. Just start walking beside them in a way that is comfortable for them. The disciples wanted to follow Jesus and He didn't demand much from His disciples at first. "Come and see."
One tidbit of psychology: If you try to push someone somewhere, their initial response will be defense, to push back. If you have been pushing your child towards Christ then they have been practicing pushing Christ away. How long have they been practicing that! Time to end that dynamic. Just be there for them. Be someone they want to follow.
That's the first step - feeling the love.