We all are God’s creatures and He loves us, but we are not all His children. What qualifies you to be called a child of God is your acceptance of the free Gift of Salvation. At that point, you are adopted into God’s Family. You also become a joint-heir with Jesus Christ. If you have been told otherwise, you need to read John 8:42, dear ones. This is why Jesus addressed certain people as the children of Satan in (John 8:44). Anyone who fills his church or ministry with your attendance, money, and charitable deeds whilst you are not yet born-again sees you just as a number. Your name is not yet in the Book of Life. God wants your heart first before He can accept anything you are giving in His Name. Waste your resources, strength and time no longer, and surrender to Jesus Christ.
The moment you surrender your life to Jesus Christ, you become part of God's Family. Other believing Christians become your brothers/sisters/beloved. You also have the privilege to call God, Father, and ask of Him all and more than you could ask of your earthly father. You also become eligible to be a partaker of all of His blessings (Galatians 3:14, Galatians 3:29).
If you have not given your life to Jesus Christ, you cannot profess Him as your Saviour and confidently say, "Amen" when prayers are uttered in His Name. Why? You cannot be called a child of God because there is an unbroken wall between you and Him, by reason of the sin of Adam and Eve which caused the human race to fall into the practice of sin. What breaks that wall is the Blood of Jesus that was shed on the Cross of Calvary. The wall is broken when you accept Him as your personal Lord and Saviour.