Mosiah 18

King Benjamin taught his people -

"...because of the covenant which ye have made ye shall be called the children of Christ, his sons, and his daughters; for behold, this day he hath spiritually begotten you; for ye say that your hearts are changed through faith on his name; therefore, ye are born of him and have become his sons and his daughters." (Book of Mormon | Mosiah 5:7)

It appears as we make the covenant of baptism, we become "born" of him and his sons and daughters. In my mind, born would suggest we are yet babes as his children for -

"Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God." (New Testament | John 3:5)

Thus we become His seed where -

"...whosoever has heard the words of the prophets, yea, all the holy prophets who have prophesied concerning the coming of the Lord—I say unto you, that all those who have hearkened unto their words, and believed that the Lord would redeem his people, and have looked forward to that day for a remission of their sins, I say unto you, that these are his seed, or they are the heirs of the kingdom of God." (Book of Mormon | Mosiah 15:11)

But at this stage, even though we may be even as small "child", we are not yet fully mature. Thus Alma taught his priests and his followers and -

"...commanded them that there should be no contention one with another, but that they should look forward with one eye, having one faith and one baptism, having their hearts knit together in unity and in love one towards another." (Book of Mormon | Mosiah 18:21)

and -

"...that the people of the church should impart of their substance, every one according to that which he had; if he have more abundantly he should impart more abundantly; and of him that had but little, but little should be required; and to him that had not should be given.
28 And thus they should impart of their substance of their own free will and good desires towards God, and to those priests that stood in need, yea, and to every needy, naked soul.
29 And this he said unto them, having been commanded of God; and they did walk uprightly before God, imparting to one another both temporally and spiritually according to their needs and their wants." (Book of Mormon | Mosiah 18:27 - 29)

It seems that as the followers of Christ continued in this manner, Alma suggests -

"...And thus they became the children of God." (Book of Mormon | Mosiah 18:22)

"Became the children of God" would then suggest a process towards growth and maturity. It seems after a life of faithfulness and covenant making, taking upon us the name of Christ, that the day will come where we will not be just children but adult sons and daughters of God and joint-heirs with Christ. Paul suggested the same saying -

"...if children, then heirs; heirs of God, and joint-heirs with Christ..."
(New Testament | Romans 8:17)