After the family moves to the daffodil-yellow villa, Theodore begins joining the Durrells on Thursdays for tea. This is partially so that he can watch the weekly seaplane land in the bay from their attic windows, a sight that delights Theodore to no end. In this way, the seaplanes come to represent the fact that, though Theodore is an adult for all intents and purposes, he has still managed to maintain a sense of childish wonder well into adulthood. Theodore has found a middle ground between stodgy, boring maturity and the unfettered curiosity that Gerry associates with childhood, turning Theodore himself into an example of someone who redefines maturity and adulthood to fit his own needs and desires.
The timeline below shows where the symbol The Seaplane appears in My Family and Other Animals. The colored dots and icons indicate which themes are associated with that appearance.
Part 2, Chapter 9: The World in a Wall
...Thursday afternoon and stays until evening. Theodore's choice to come on Thursdays is purposeful: the seaplane from Athens lands on Thursdays in a bay not far from the Durrells' villa, and... (full context)