While we are all children of God in the sense that God created every single one of us, God has also chosen those He will have an intimate, special, and privileged relationship with. This is a filial relationship, one that is not bestowed on us because of our own merit or good-ness, it's bestowed to us as a gift through Jesus Christ.
Jesus' death made way for the Holy Spirit to do His work, by opening our spiritual eyes to the new reality of being a new creation, a new child of God. Without this divine intervention, we would never be able to receive God in the way He intended for us. When we receive the name of Jesus, as in we believe He is who He says He is, we are adopted into God's family and have all rights to His holy inheritance, love, and tender, unfailing care.