The correct option is D Didn't they try?
The tense of a sentence denotes a time, whether it is the time now (present), time then (past) or the time to come (future). The verb of a sentence has most to do with the tense. The simple future tense refers to an action that is yet to take place, in the future, the verb is often preceded by 'will' to refer to the future. Option A is in the future tense, "will go" that refers to the action which is yet to take place. In B, 'won't' is a contraction of 'will not', 'Will they not try?', 'will' refers to the future. In option D, the future event is stated "will not eat", the baby 'will not' eat his soup. A, B and D are hence, in the simple future tense. We need to choose an option which is not in the future tense. In option C, 'didn't' is a contraction of 'did not', 'did' is in the past tense, referring to an action that took place in the past. Hence option C is correct, as it isn't in the simple future tense, and options A, B and D are incorrect.