Translation:A couple of children are playing in the park.
"pair" can be either singular or plural in English and usually depends on a larger context. "A pair of jean is" always "A pair of contestants are" or a "A pair of contestants is" actually connote different things. The singular usage implies they are from the same team or are working together the plural implies they are competing against one another. "A pair of children is" or "A pair of children are" are both acceptable and usually the singular would connote familiarity.