Final answer:
Wendy and Peter, not Joules and Kevin, were the children who returned home on their own, likely dropped off by a helicopter after an outing where they had strawberry ice-cream and hot dogs.
Step-by-step explanation:
The Rockman parents did not actually drop off Joules and Kevin anywhere as there are no characters by those names in the provided reference. Instead, the children, Wendy and Peter, seem to have returned home on their own after a trip. The passage indicates that they arrived happily in the front door, with a smell of fresh air and talking about their trip in the helicopter, suggesting that they were dropped off by a helicopter, not by their parents.
Their mention of being full of strawberry ice-cream and hot dogs implies they were at some sort of event or outing where such foods were available. However, without more context, we cannot determine the exact location where Wendy and Peter were prior to arriving home.