If thou canst believe, all things are possible to him that believeth. Pray persistently and patiently, as did the widow in Luke . Pray for the Lord to use someone else to reach them. Share spiritual truth if they will listen. Be careful not to be pushy or drown them with information.
Little bites are better.
Be willing to listen to them. Be a good example. Even after children are grown, they still watch and learn from the pattern of their parents. Don't spend all your time pining over past mistakes. If you want your religion to be attractive to your kids, then be as positive and joyful as you can.