"We should bear in mind and realize that when we call God our Father we ought also to act like sons. If we are pleased to call him Father, let him in turn be pleased to call us sons. We should life like the temples of God we are, so that it can be seen that God lives in us."St. Cyprian

Once we are baptized and adopted by by God as his sons ad daughters, we remain such eternally. We ,may deny and reject him but he will never deny us.  The Prodigal Son while he left his father and rejected his relationship with the father, the father  still considered him his son. The burden of proof of relationship rests not on the Father but on us his sons and daughters. The father of the Prodigal Son waited for him. It was up to the son to return and call him father again. If we call God our Father, then we should seek to live as sons and daughters in relationship with Him.