How does "All Summer in a Day" begin?

The story begins with the children looking outside at the rain and discussing the sun coming out.

The story takes place on Venus.  It rains almost all the time.  In fact, the sun has not come out for seven years.  At the beginning of the story, a group of nine-year-old children is looking outside at the rain discussing the imminent presence of the sun.

"Ready ?"

"Ready."

"Now ?"

"Soon."

"Do the scientists really know? Will it happen today, will it?"

"Look, look; see for yourself!"

The children pressed to each other like so many roses, so many weeds, intermixed, peering out for a look at the hidden sun.

The children are excited because they were so young when the sun came out last that they barely remember it.  It is a really special occasion.  We are introduced to a girl, Margot, who is from Earth.  Unlike the other children, she has seen the sun recently and remembers it.  This makes her somewhat of an outcast.

Margot stood apart from them, from these children who could ever remember a time when there wasn’t rain and rain and rain. They were all nine years old, and if there had been a day, seven years ago, when the sun came out for an hour and showed its face to the stunned world, they could not recall.

The children think that the rain is starting to stop.  This is important because they always argue and fight with Margot.  They bully her, and she keeps herself separate and apart from them.  You would think, though, that this reappearance of the sun would bring the group together.  It won’t.  The children target Margot because she is different.

Bradbury starts the story with the brief lines of dialogue to create suspense.  We do not know what the children are so excited about at first.  The sun coming out for the first time in years is very important to the story, because it demonstrates the children’s cruelty when they don't let Margot see it.