---------(C) A new phenomenon visible at Managua’s major intersections is waves of vendors and beggars, many of them children, who [mob cars at the stoplights]
But I still do not understand the last part of C. When I put it in the sentence.I am confused by " many of them children,who" how to connect [ mob cars at the stoplights. In meantime, what's the meaning about " many of them children",