Why is He called God’s “only begotten Son,” since we also are the children of God?

Heidelberg Catechism

~His Deity

Question 33. Why is He called God’s “only begotten Son,” since we also are the children of God?

Answer. Because Christ alone is the eternal, natural Son of God,[1] but we are children of God by adoption, through grace, for His sake.[2]

[1] Jn 1:1-3, 14, 18, 3:16; Rom 8:32; Heb 1; 1 Jn 4:9;
[2] Jn 1:12; Rom 8:14-17; Gal 4:6; Eph 1:5-6; 1 Jn 3:1