Believing Children at Ephesus and Colossae - EPHESIANS is a letter addressed to the saints at Ephesus. Paul described them as having redemption through the blood of Christ and forgiveness of sins (Eph. 1:1,7). Therefore, the original recipients of this letter were believers in Christ. Towards the end of the letter, Paul addressed directly different groups of believers in Ephesus on how they could walk in a way worthy of their calling as saints (c.f., Eph. 4:1). Children (teknon in Greek) are commanded to obey (in the Lord) their parents. Teknon refers to a child of either sex [Strong's Exhaustive Concordance, www.e-sword.net, Version 7.9.8]. The fact that Paul addressed children means that these children were saints - believers in Christ as this letter was addressed to the saints at Ephesus. If there were children who believed in Christ at Ephesus at that time then children today can also trust in Christ.
The above same reasoning can be applied to the letter of COLOSSIANS
and the same conclusion reached – that the children addressed must have been believers. Colossians was addressed to saints and faithful brethren in Christ at Colossae. Paul described them as people who were delivered from the domain of darkness and transferred into the kingdom of Christ in whom they have redemption, the forgiveness of sins (Col. 1:13-14). In other words, they were believers in Christ. In Col. 3:20, children (teknon in Greek) are addressed and commanded to be obedient to their parents in all things. Therefore, there were believing children at Colossae. The application for us is that since children can be believers, we must share the Gospel with them.
The phrase "in the Lord" in Eph. 6:1 does not imply that children are to obey their parents only in those matters that are consistent with Scriptures because then the children would have to be Bible scholars! Moreover, Paul also taught that children are to obey parents in everything (Col. 3:20). A similar phrase “as to the Lord/Christ” is found in Eph. 5:22 and 6:5 when Paul addressed wives (to submit to their husbands) and slaves (to obey their masters). It is probable that when Paul commanded children to obey their parents in the Lord, he meant that as believers, children are to obey their parents even non-believing parents. This is their duty as believers. Obedience to parents is right (Eph. 6:1) and well-pleasing to the Lord (Col. 3:20).