Final answer:
Aven's dad gave the family free ice cream and t-shirts to show appreciation for Aven's help in fixing something in the machinery.
Step-by-step explanation:
In the story, Aven's dad had to give a family free ice cream and t-shirts because Aven fixed something in the machinery. The quote 'He may have got into the machinery and fixed something' suggests that Aven's dad had to give the family the freebies as a way of thanking Aven for his help. Although Peter, Aven's brother, didn't know much about machinery, Aven was described as a wise child with a high IQ, which implies that he was able to fix something important.
The children, Wendy and Peter, came home happily with bright blue eyes and a smell of fresh air on their clothes from their trip. They mentioned that they were full of strawberry ice cream and hot dogs. Therefore, it can be assumed that they were the lucky recipients of the ice cream and t-shirts.