1 Cor 4:15-16: Even though you have ten thousand guardians in Christ, you do not have many fathers, for in Christ Jesus I became your father through the gospel. Therefore I urge you to imitate me (NIV).
In this passage, Paul talks about the importance of a father's example. While there may be lots of good Christian examples for your children, the person they are most likely to imitate is their earthly father. For their sakes you must practice what you preach because your children are going to be greatly influenced by the things you do, the way you talk, what you watch, etc. You are their model for adult behavior.
Negative and positive traits are passed from father to son. That's why there are so many second and third generation addicts and abusers. Strive to minimize the negative traits and accentuate the positive. Pass down a zeal for following Christ. And remember, your kids are much more likely to follow what you do than what you say.
Practice what you preach.