The Greek text of John 3.16 calls Christ "monogenes" which has traditionally been rendered "only begotten son" (KJV, and those in that translation family) or "his one begotten Son" (Wycliffe's translation).
The force of monogenes is that Christ is the one "natural born" son of God. We, in turn, in the waters of Baptism become God's children, not by "natural birth," but by adoption. God graciously takes us who were born in sin, children of the devil, and adopts us into His own family.
In the last 50 years, it has been argued that people do not and cannot understand this argument, and that Christians who are otherwise intelligent cannot understand the force of the word "begotten." So we have a number of translations just ignoring the Greek text, and calling Christ "God's only son," or "his one and only son." (See examples at the end).
Which begs the question: if we are indeed the children of God (per Eph. 1.5, Romans 8.14-16, and Galatians 4.4-6) how can Christ be God's "only son"?
Of course, Christ is not God's only son: God has innumerable (Rev. 7.9) children, all of whom are really God's children. Really. Not imaginary, not honorary, but children of God.
All of which leads us to the question: why are we using translations which deliberately mis-translate John 3.16? The concept of "begottenness" isn't that complex to explain briefly. And ignoring "monogenes" confuses so much: the divine nature of Christ, the human nature of Christ, our nature as God's children, and the concept of adoption (both natural and spiritual).
The LCMS bit into the NIV virus for some 25 years, and has now bitten into the equally damaging ESV. All of which means that those who continue to use the ESV must carefully correct this and other errors that continue in our midst.
NIV: "his one and only Son" (footnote: "Or his only begotten Son")
NASB: "only begotten Son"
The Message: "his one and only Son"
Amplified: "His only begotten ([a]unique) Son"
New Living: "his one and only Son"
ESV: "his only Son"
CEV: "his only Son"
NKJV: "His only begotten Son"
New Century: "his one and only Son"
21st Century KJV: "His only begotten Son"
ASV: "his only begotten Son"
NIV--UK: "his one and only Son"
TNIV: "his one and only Son"