In Anita Desai's short story "Games At Twilight," how does the writer vividly present the children in the story's opening?

The author effectively uses a number of various descriptors and figures of speech to indicate the children's emotions and actions and to graphically convey what they looked like. In effect, she appeals to the reader's senses and wishes us to indulge in these frantic and frenzied moments just before the children's release from the stuffy and stifling interior of the house into the exhilarating freedom outside.

In the second sentence, we learn that the children had been fed and groomed. They "had had their tea, they had been washed and had their hair brushed." The children were fed and clean, ready to face the challenges and excitement outside. They had been confined to the house the entire day since it had been too hot to play outside. They were impatient since the basics had been attended to. They were brimming with energy and ready to get dirty, as it were.

The author tells us that "the children strained to get out." The sentence conveys their impatience. They had been restricted for so long that they were, at that moment, striving hard to go outside, even to the point of exertion. The words "red" and "bloated" emphasize the effort the children put into their attempts to get out. They were like caged animals striving for freedom. 

Furthermore, the author expresses how stifling the atmosphere was inside by mentioning that the children found it hard to breathe. It "made them feel that their lungs were stuffed with cotton wool and their noses with dust." The only way it which they would feel comfortable would be if "they burst out into the light and see the sun and feel the air." The word "burst" suggests an explosive action. Once the children are let go, they will explode into the outside. If not, they will "choke."

The author makes it clear that the children do not even consider the mother's concern to safeguard them from the harsh sun. They just want to be out and beg her to let them go, making a promise that they will obviously be unlikely to keep, even though they counter the mother's unfinished phrase by stating that they will not leave the porch, as she evidently believes they will. 

Their pleading culminates in a what the writer describes as horrendous wailing. One can imagine the sound as being akin to the caterwauling of cats during the dead of night. Their terrible crying is what convinces the mother to let them out. Once the door is open, the children rush out "like seeds from a crackling, over-ripe pod into the veranda." The simile is quite apt and effectively describes their frenzied and uncontrolled rush to the outside. Once they are in the open, the children express their delight by screaming wildly and loudly, like a bunch of maniacs. They are ecstatic. 

The introductory paragraph evocatively conveys the exuberant nature of children. They possess a vitality that adults find difficult to understand. The introduction distinctly indicates how keen they are to be active and how much they despise being restricted. They wish to enjoy the freedom of the outside where they can truly indulge themselves. In addition, the introduction also establishes a contrast to the much more subdued situation conveyed later in the story, where the focus is more singular.