Eph:6:1: Children, obey your parents in the Lord: for this is right. Eph:6:2: Honour thy father and mother; (which is the first commandment with promise;) Eph:6:3: That it may be well with thee, and thou mayest live long on the earth. Eph:6:4: And, ye fathers, provoke not your children to wrath: but bring them up in the nurture and admonition of the Lord.

Here St. Paul previously a zealous Jew himself, is not introducing a new commandment, but is reminding in 6:2 of the age old command that was practiced by children from 8 days old.

The persons to whom this epistle is sent: To the saints who are at Ephesus, that is, to the Christians who were members of the church at Ephesus, the metropolis of Asia. He calls them saints, for such they were in profession, such they were bound to be in truth and reality, and many of them were such. He calls them the faithful in Christ Jesus, believers in him, and firm and constant in their adherence to him and to his truths and ways. Those are not saints who are not faithful, believing in Christ, firmly adhering to him, and true to the profession they make of relation to their Lord. Note,

This command is of course applicable to infants as well from the beginning that it was given through Moses to Israel. It is even an universally in force command. They are to obey their parents. In the OT children were subject to this command ‘with a promise’ from the age of 8 days old.

Master & corresponding Servant, Wife & husband, Children and parents. Only children a commandment here, and are given only this commandment denoting of what age these are. i.e. in the beginning stages of life and in the care of their parents. Children of the age group as to be ‘nurtured’ or under the care or upbringing of parents and as 6:4 suggests children being ‘nurture’d and  brought up in the admonition of the Lord (something like Timothy). And this, the apostle says is to be obeyed ‘in the Lord’

Some point out that this passage does not imply that the children addressed are surely not babes, but old enough to hear and obey the apostolic command, and hence old enough to have heard and obeyed Christ. But the parents addressed here to bring up the children is addressed not as ‘parents of children old enough’ but just ‘parents’ in general. Not that only children who have reached the age have to be brought up in Christ.

Any Protestant preacher, when preaching on this verse will of course when addressing a congregation with infants or children not reached the age of reason will he not include this age group as well into context or will he say, by the way this command is not applicable to infants and those not reached the age of reason.

To obey parents is not something that is to be imputed in children at an elder age but from the beginning.

6:2 clearly shows that this command is not a new one but part of the Ten commandments, one to which every child of the Old Testament was subject to from 8 days old when they become part of God’s covenant..

King James Bible
Children, obey your parents in the Lord: for this is right.

Strong's Transliteration Greek English Morphology

5043 [e] tekna τέκνα Children, N-NNP

2962 [e] kyriō κυρίῳ [the] Lord; N-DMS

Children - τέκνα tekna This word usually signifies those who are young; but it is used here, evidently, to denote those who were under the care and government of their parents, or those who were not of age.

Obey your parents - This is the first great duty which God has enjoined on children. It is, to do what their parents command them to do. The God of nature indicates that this is duty; for he has impressed it on the minds of all in every age; and the Author of revelation confirms it. It is particularly important because the child is not competent as yet; to "reason" on what is right, or qualified to direct himself; and, while that is the case, he must be subject to the will of the parents.

It is important, because the family government is designed to be an imitation of the government of God. The government of God is what a perfect family government would be; and to accustom a child to be obedient to a parent, is designed to be one method of leading him to be obedient to God. No child that is disobedient to a parent will be obedient to God; and that child that is most obedient to a father and mother will be most likely to become a Christian, and an heir of heaven.

 ‘in the Lord’ -Both parents and children being Christians "in the Lord," expresses the element in which the obedience is to take place, and the motive to obedience.

Every protestant understands and acknowledges that the second part is universally applicable to all children irrespective of their age. Or is the apostle asking only for the children who have reached the age of reason to be brought up in the nurture and admonition of the Lord.

De:29:1: These are the words of the covenant, which the LORD commanded Moses to make with the children of Israel in the land of Moab, beside the covenant which he made with them in Horeb.

De:29:9: Keep therefore the words of this covenant, and do them, that ye may prosper in all that ye do. De:29:10: Ye stand this day all of you before the LORD your God; your captains of your tribes, your elders, and your officers, with all the men of Israel,De:29:11: Your little ones, your wives, and thy stranger that is in thy camp, from the hewer of thy wood unto the drawer of thy water: De:29:12: That thou shouldest enter into covenant with the LORD thy God, and into his oath, which the LORD thy God maketh with thee this day:De:29:13: That he may establish thee to day for a people unto himself, and that he may be unto thee a God, as he hath said unto thee, and as he hath sworn unto thy fathers, to Abraham, to Isaac, and to Jacob.De:29:14: Neither with you only do I make this covenant and this oath;De:29:15: But with him that standeth here with us this day before the LORD our God, and also with him that is not here with us this day:

Christ Reigns!!