A street performer is entertaining a gathered audience with the help of a young boy.
A street performer and young boy are entertaining passersby.
It is implied that the performer and young boy are entertaining an audience of passersby because there is no mention of a pre formed audience.
Since the entertainer is a street performer, the audience are passersby.
A Street performer entertaining with the help of a young boy is the same as the two working together to entertain.