If I disobeyed my earthly father, I was still his daughter. Everyone one sins. God adopts some of us even though we haven't earned that adoption. It can't be earned.
If we were already God's children, adoption would be unnecessary.
Mormonism, on the other hand, teaches that those He first calls children, can be disowned:
Who desires to enter the eternal world and be a servant, when the promise is held out that we may be sons and daughters of God? Yet there will be the vast majority who will enter into the eternal world as servants, and not as sons, and this simply because they think more of the world and its covenants, than they do of God and his covenants; simply because in their blindness of heart, they refuse to keep these sacred and holy commandments. Oh, what bitterness there will be in the day of judgment, when every man receives his reward according to his works!
http://ldsseminary.files.wordpress.com/2013/01/doctrines-of-salvation-volume-2.pdf
“The ordinances of the temple, the endowment and sealings, pertain to exaltation in the celestial kingdom, where the sons and daughters are. The sons and daughters are not outside in some other kingdom. The sons and daughters go into the house, belong to the household, have access to the home. ‘In my Father’s house are many mansions’ [John 14:2]. Sons and daughters have access to the home where he dwells, and you cannot receive that access until you go to the temple. Why? Because you must receive certain key words as well as make covenants by which you are able to enter. If you try to get into the house, and the door is locked, how are you going to enter, if you haven’t your key? You get your key in the temple, which will admit you.“. . . You cannot find a key on the street, for that key is never lost that will open the door that enters into our Father’s mansions. You have got to go where the key is given. And each can obtain the key, if you will; but after receiving it, you may lose it, by having it taken away from you again unless you abide by the agreement which you entered into when you went into the house of the Lord.”
Joseph Fielding Smith, Doctrines of Salvation, 2:40–41