Who are God's children? Spiritual birth makes someone a child of God. It's in the Bible, John 1:12-13, NIV. "To all who received Him, to those who believed in His name, He gave the right to become children of God—children born not of natural descent, nor of human decision or a husband's will, but born of God."
God offers us the opportunity to be His children. It's in the Bible, I John 3:1, NIV. "How great is the love the Father has lavished on us, that we should be called children of God! And that is what we are! The reason the world does not know us is that it did not know Him."
Christians are adopted into God's family. It's in the Bible, Romans 8:16, NIV. "The Spirit Himself testifies with our spirit that we are God's children." Galatians 4:4-5, RSV. "But when the time had fully come, God sent forth His Son, born of woman, born under the law, to redeem those who were under the law, so that we might receive adoption as sons."
Take a lesson from the children. It's in the Bible, Luke 18:16-17, TLB. "Then Jesus called the children over to Him and said to the disciples, 'Let the little children come to me! Never send them away! For the Kingdom of God belongs to men who have hearts as trusting as these little children's. And anyone who doesn't have their kind of faith will never get within the Kingdom's gates."