The children of light are genuine believers in God's anointed one

John 12:36
Believe in the light while you have the light, so that you may become children of light.

Ephesians 5:8-13
For you were once darkness, but now you are light in the Lord. Live as children of light (for the fruit of the light consists in all goodness, righteousness and truth) and find out what pleases the Lord. Have nothing to do with the fruitless deeds of darkness, but rather expose them. It is shameful even to mention what the disobedient do in secret. But everything exposed by the light becomes visible—and everything that is illuminated becomes a light.

1 Thessalonians 5:4-9
But you, brothers and sisters, are not in darkness so that this day should surprise you like a thief. You are all children of the light and children of the day. We do not belong to the night or to the darkness. So then, let us not be like others, who are asleep, but let us be awake and sober. For those who sleep, sleep at night, and those who get drunk, get drunk at night. But since we belong to the day, let us be sober, putting on faith and love as a breastplate, and the hope of salvation as a helmet. For God did not appoint us to suffer wrath but to receive salvation - deliverance through our Lord Jesus God's anointed onet.

The apostle John also uses this metaphor of light and darkness to contrast the life of believers with that of unbelievers. See 1 John 1:5-7 and 1 John 2:8-10.

1 John 1:5-10: This then is the message which we have heard of him, and declare unto you, that God is light, and in him is no darkness at all. If we say that we have fellowship with Him, and walk in darkness, we lie, and do not the truth: But if we walk in the light, as He is in the light, we have fellowship one with another, and the blood of Jesus, God's anointed one cleanses us from all sin. If we say that we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, He is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness. If we say that we have not sinned, we make Him a liar, and his word is not in us.

1 John 2:8-11: Again, a new commandment I write unto you, which thing is true in him and in you: because the darkness is past, and the true light now shines. He that says he is in the light, and hates his brother, is in darkness even until now. He that loves his brother abides in the light, and there is none occasion of stumbling in him. But he that hates his brother is in darkness, and walks in darkness, and knows not where he goes, because that darkness has blinded his eyes.