He that teacheth his son grieveth the enemy: and before his friends he shall  rejoice of him.  (Ecclesiasticus 30:3) 

Many teach their children about worldly politics, others teach them to speak foreign languages: French, German, Italian, and in this spend no trifling sums. Others endeavor to teach them commerce and other arts. But hardly anyone teaches them to live in a Christian manner. However, without this, all learning is nothing and all wisdom is madness. For what does it profit a Christian to speak Italian, French and German, if he lives in an ungodly manner? What use is it to be skilled in commerce and the arts if one lacks the fear of God? God will not ask you whether you taught your children French, German or Italian or the politics of social life–but you will not escape divine reprobation for not having instilled goodness into them. I speak plainly but I tell the truth: if your children are bad, your grandchildren will be worse, and the evil will thus increase…and the root of all this is our thoroughly bad education  — St. Tikhon of Zadonsk 

Have great care of your children. We live at a time when much freedom is given to the expression of thought, but little care is taken that thoughts should be founded on truth. Teach them to love truth.      –Elder Macarius of Optina