To begin, keep in mind that we are all sinners. Nobody is born believing in Christ. Disbelief and pride, rather, are the default settings of fallen humanity. Your child, unfortunately, is not an exception.
Add to that the fact that as they try to figure out the world and their place in it, young adults naturally challenge the status quo and seek to assert their independence.
As people mature, their peers begin to have a greater influence on their perspectives, while their parents’ influence diminishes. Peers frequently reward a youngster who begins to challenge or question the status quo.
What one must understand is that their faith must ultimately be their own. Faith in Christ is not something that is inherited.
Second, try to figure out why they don’t believe. The natural instinct may be to jump right in and show them why they are wrong and why they should change their minds and follow Christ.
However, the underlying issue is not always one of ignorance or incorrect information.