Technically, Biblically, no.
We’re certainly all God’s creation, but the children thing is different. Coming to Christ, becoming a Christian, is considered part of an adoption process, according to the Bible.
Romans 8:15 says “For you did not receive the spirit of bondage again to fear, but you received the Spirit of adoption by whom we cry out, ‘Abba, Father.’” (There are other adoption scriptures as well.) God, by His Spirit, brings us into His family according to the same model that the ancient Romans would have understood—taking into one’s family someone who is not naturally part of the family, able now to receive the name and privileges of being a part of that family.
In speaking of God’s coming to earth in Christ, the book of John says this: “But as many as received Him [meaning Jesus Christ], to them He gave the right to become children of God, to those who believe in His name” (John 1:12). So being a child of God is not something that happens when you’re born. It comes when you’re born again, and it’s granted to you then by God.
From the Bible’s point of view, every human being is a creation of God, even being created in His image (which has unfortunately since been twisted and stained by the presence of sin in our lives). But from a Christian point of view, only those who “receive Him” are considered His children.