"Parents should endeavor to keep out of the home every influence that is not productive of good. In this matter some parents have much to learn. To those who feel free to read story magazines and novels I would say: You are sowing seed the harvest of which you will not care to garner. From such reading there is no spiritual strength to be gained. Rather it destroys love for the pure truth of the word. Through the agency of novels and story magazines, Satan is working to fill with unreal and trivial thoughts, minds that should be diligently studying the word of God. Thus he is robbing thousands upon thousands of the time and energy and self- discipline demanded by the stern problems of life. CT 120"
"Be not deceived; God is not mocked: for whatsoever a man soweth, that shall he also reap."
The EGW passage directly uses the sowing and reaping metaphor, which is the core of Galatians 6:7. The context of sowing negative influences and reaping a negative harvest makes the connection clear.
"Parents, guard the principles and habits of your children as the apple of the eye. Allow them to associate with no one with whose character you are not well acquainted. Permit them to form no intimacy until you are assured that it will do them no harm. Accustom your children to trust your judgment and experience. Teach them that you have clearer perception of character than they in their inexperience can have, and that your decisions must not be disregarded. CT 120.2"
"Keep thy heart with all diligence; for out of it are the issues of life."
Both passages emphasize the importance of guarding the heart/principles of children and being diligent in protecting them from harmful influences. The 'apple of the eye' metaphor reinforces the need for careful protection.