"Fathers and mothers, do not forget that children learn more by the eye than they do by the ear. No school will make such deep marks on character as home. The best of schoolmasters will not imprint on their minds as much as they will pick up at your fireside. Imitation is a far stronger principle with children than memory. What they see has a much stronger effect on their minds than what they are told.
Take care, then, what you do before a child. It is a true proverb, "Who sins before a child, sins double." Strive rather to be a living epistle of Christ, such as your families can read, and that plainly too. Be an example of reverence for the Word of God, reverence in prayer, reverence for means of grace, reverence for the Lord's day. Be an example in words, in temper, in diligence, in temperance, in faith, in charity, in kindness, in humility. Think not your children will practice what they do not see you do. You are their model picture, and they will copy what you are. Your reasoning and your lecturing, your wise commands and your good advice; all this they may not understand, but they can understand your life."
Read more here.