They are unfaithful to Yahweh; For they have borne illegitimate children. Now the new moon will devour them with their fields.
Keil and many others have pointed out that the background of this whole prophecy is the covenant relationship that existed between God and Israel. The "strange children," or "bastards" as in New English Bible, are one with the "children of whoredom" mentioned earlier in the prophecy, which Gomer bore to Hosea, violating a marriage contract.  That contract, in the larger theater of God's relationship with Israel, was the covenant outlined in the Pentateuch, the Decalogue, etc.  Israel had violated their covenant with God in their failure to rear believing children in the fear and knowledge of the true God. Instead, they were being reared as children of the old Canaanite bull-god, answering to the "spiritual adultery" which is the principal theme of Hosea's prophecy.