The title might suggest that the story explores the themes of childhood, toys, and the ephemeral nature of summer, with the 'last all summer long' part adding a sense of duration and significance to the toys' role in the narrative.
Hard to say for sure. You'd have to look at the details and settings in the comic to determine if it's summer. Maybe the characters' clothing or the scenery could give a clue.
A fanfic of 'All Summer in a Day' could explore many aspects. It might expand on the characters' emotions during that brief moment of sun. For example, Margot, who has a deeper connection to the sun, could be further developed. The author of the fanfic might describe in more detail how she feels when she finally sees the sun again after years of rain.
One significant theme in a 'All Summer in a Day Fanfic' could be isolation. Margot is isolated in the original story because of her different experiences. A fanfic could further explore this isolation, perhaps by showing how she copes with it when the other children shun her. It might also show how her isolation affects her view of the world around her.
In 'All Summer in a Day', the children are excited for the rare appearance of the sun. But they're mean to Margot. It shows how cruel kids can be and what it's like to long for something you rarely have. It's a poignant story with deep messages.