At Weathertop, did the Nazgul fear Frodo?

The sense I get from the Weathertop scene is not fear but one of "caution". It's understandable that the Nazgul would exercise a certain caution as they approached Frodo. They don't know much about hobbits and he is holding the most concentrated source of power in the land. Imagine a group of police approaching a young child holding a loaded gun. They were intent on capturing the ring from him, but not entirely sure of the situation. He had, after all, already eluded them on several occations and was known to be in the company of a Ranger.