"I am about to put obstacles in front of this people." Yahweh speaks of the troubles that he will make happen to the people of Israel as if they were a blocks that people stumble over. (See: [[rc://en/ta/man/jit/figs-metaphor]])
The phrase "will stumble" is understood from the previous phrase. Alternate translation: "fathers and sons will both stumble" or "fathers and sons will both be hurt" (See: [[rc://en/ta/man/jit/figs-ellipsis]])