Possible meanings are 1) "Because we are the children of God and because the world did not know God, it does not know us" or 2) "Because the world did not know God, it does not know us."
Here "the world" refers to people who do not honor God. What the world did not know can be made explicit: Alternate translation: "those who do not honor God do not know that we belong to God, because they did not know God" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-explicit]])