Answer:
The first one "they were happy to go to the fair, where they could play games."
Step-by-step explanation:
The first part says "they were happy to go to the fair" with "were" being in present form (past form would be 'was', future form would be 'would'). The second half says "where they could play games." and 'could' is in future tense.
The first half has a present tense verb while the second half has a future tense verb. So the answer is 1.