Wonderfully moving commentary by John Calvin on Ephesians 6:4 “And you, fathers, do not provoke your children to wrath, but bring them up in the training and admonition of the Lord.” where he says that “bring them up in” should be understood as “let them be fondly cherished in”.
Parents, on the other hand, are exhorted not to irritate their children by unreasonable severity. This would excite hatred, and would lead them to throw off the yoke altogether. Accordingly, in writing to the Colossians, he adds, “lest they be discouraged.” (Col 3:21.) Kind and liberal treatment has rather a tendency to cherish reverence for their parents, and to increase the cheerfulness and activity of their obedience, while a harsh and unkind manner rouses them to obstinacy, and destroys the natural affections. But Paul goes on to say, “let them be fondly cherished;” for the Greek word, (ἐκτρέφετε,) which is translated bring up, unquestionably conveys the idea of gentleness and forbearance. To guard them, however, against the opposite and frequent evil of excessive indulgence, he again draws the rein which he had slackened, and adds, in the instruction and reproof of the Lord. It is not the will of God that parents, in the exercise of kindness, shall spare and corrupt their children. Let their conduct towards their children be at once mild and considerate, so as to guide them in the fear of the Lord, and correct them also when they go astray. That age is so apt to become wanton, that it requires frequent admonition and restraint.
– Calvin’s Commentaries, Vol. 41: Galatians and Ephesians