What if you have adult kids that have walked away from Christianity?
Number one, you have to pray regularly for them.
Number two, ask them what they believe and why they believe it. Then, listen patiently. Create a space in your relationship where they feel safe to have these conversations.
Lastly, ask permission to offer your thoughts. If you’ve allowed them to open up, they’ll be more willing to receive your input. Be patient, and expect that this dialogue may take years.