Adam Clarke on Ephesians 6:1

Children, obey your parents - This is a duty with which God will never dispense; he commands it, and one might think that gratitude, from a sense of the highest obligations, would most strongly enforce the command.

In the Lord - This clause is wanting in several reputable MSS., and in same versions. In the Lord may mean, on account of the commandment of the Lord; or, as far as the parents commands are according to the will and word of God. For surely no child is called to obey any parent if he give unreasonable or unscriptural commands.