John 1:12 says:
But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name:

If you have received Christ into your heart and you believe in His name, not just in word, but in deeds such that everyone around you can see from your lifestyle that you are a believer in Christ, then you qualify to be called a child of God.

On the other hand, the Bible says that the devil has his own children too. Jesus Christ was addressing the Pharisees and He said to them in John 8:44:

Ye are of your father the devil, and the lusts of your father ye will do. He was a murderer from the beginning, and abode not in the truth, because there is no truth in him. When he speaketh a lie, he speaketh of his own: for he is a liar, and the father of it.

The question then is, how do we tell a child of God apart from a child of the devil? The Bible answers this question aptly. For example, the Bible says that people who love the world do not have the love of God in them (1 John 2:15-16). This clearly implies that such people cannot be described as God’s children. When you see someone who loves material things more than God, that fellow does not have the love of God in him and hence cannot be His child if he or she remains in that state.

A child of God on the other hand is one who is born of the Spirit and focuses on spiritual things rather than worldly things. John 3:3-7 says that anyone who wants to enter into the kingdom of God must be born of the Spirit, and of course, only the children of God can enter into His kingdom. This is why you must be born again.

Beloved, when you are born again, you are born of the Spirit, and you truly become a child of God. When you are born of the Spirit, you will begin to live by the Spirit and be led by Him. You will begin to exhibit the fruit of the Spirit as written in Galatians 5:22-23. Remember, it is the kind of fruit you produce that will determine who your father truly is.
Written by Pastor E.A. Adeboye.