Teach your kids how everything of value in life is found in God.
Teach them consecration: how we derive our purpose from God's purpose.
When kids get around ten years old, this can take on more explicit forms.
Around this age, you can show your kids how to lay out a life plan and how to focus their lives on a transcendent purpose.
A template that seems to work well is to draw a triangle, and divide it into three sections. From top to bottom: vision, goals, means. A vision ought to be no more than a sentence and encapsulate what is most important to them. The goals are specific measurable achievements that define successful accomplishment of the vision. Means define you are going to do and how often in order to achieve your goals.
When you catch them doing something that doesn't align with their vision, you can ask them to go read it and think about what they really want, and either change their behavior or their vision.