Peanut gallery

Pea·nut gal·ler·y

The cheapest seats in a theater, being typically those farthest from the stage, as in the uppermost balcony.
In a television show for children, the section where visiting children sit as guests during the performance.
Any group of children, or the chidren in a group of people; as, let's have no noise from the peanut gallery. [Colloq.]