A mange les bonbons ? Les enfants

Qui or Ou

Qui

Explanation:

Qui means who in English. We can resort this answer because the answer is referring to people. Les enfants means the children in English.Another method to verify your answer is:"Who ate the sweets?" makes sense when compared to using où, which means where in English."Where ate the sweets?" does not make sense; therefore, your answer is qui.