Final answer:
The children must be old enough to be considered as paying adults for the tour.
Step-by-step explanation:
To determine what must be true about the ages of the children, we need to analyze the given information. Mr. Wagner paid $123 for a tour of the Everglades on an airboat for himself, his wife, and two children. Since the total cost of the tour was $123, we can divide it equally among the four people. Therefore, each person's share would be $123 divided by 4, which is $30.75.
Now, since the cost is divided equally, it indicates that the children are sharing the same cost as the adults. Therefore, it must be true that the ages of the two children are such that they are considered as paying adults for the tour. This means that both children are old enough to be included in the count of adults, usually 12 years or older.