People who say this are slightly mistaken. What they are really trying to say here is that God created everyone on earth. God is the Father in the sense that He formed us and gave us life, but unless we choose to give our life to Him we are not yet His children. God is a relational being and needs us to come to Him. When we accept that Jesus sacrificed His life for us and welcome that into our hearts, we then can become His children the way the Bible explains. In Romans 8:15-16 it says “But you have received the Spirit of adoption as sons, by whom we cry, ‘Abba! Father!’ The Spirit himself bears witness with our spirit that we are children of God.”