How do the children in this story react to the long-awaited event in "All Summer in a Day?" Did their behavior surprise you?

The children are excited and anxious about the arrival of the sun, and they respond by bullying the girl who has seen it more recently than they have.

I wish I could say that the behavior of the children in this story surprises me and no children on Earth would ever act this way.  Unfortunately, bullying is an everyday occurrence on our planet and all Bradbury did was set the story on Venus during a rainstorm.  Otherwise, the story could have happened anywhere and anytime.

Kids get anxious when they are expecting something.  Even if the thing they are expecting is something positive and something they really want to happen, their behavior leading up to the event can sometimes be inappropriate.  That is just the way kids are. 

The kids in this story were really excited that the sun was coming out for the first time in recent memory, the first time in seven years, and they act out. 

"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. It rained. 

In addition to being excited, the children target Margot.  Margot has seen the sun recently because she came from Earth more recently than the other children.  She is different, and the other kids do not like different.  Kids in general do not like different.  This is why they lock Margot in the closet during the time the sun comes out.  They start to get more and more excited, anticipating, and they take it out on her.

"Nothing’s happening today. Is it?"

They all blinked at him and then, understanding, laughed and shook their heads.

"Nothing, nothing!"

"Oh, but," Margot whispered, her eyes helpless. "But this is the day, the scientists predict, they say, they know, the sun…"

Even though she has seen the sun more recently than anyone else, or maybe perhaps she has, Margot is one of the most anxious to see the sun.  She really misses it.  The kids take their jealously towards her and their excitement over the event and funnel that energy into the very inappropriate plan of shoving her in the closet so she misses the sun.