"The Ball Room" is a short story by China Miéville, co-authored by Emma Bircham and Max Schaefer. It was first published in the 2005 collection Looking For Jake. In 2006 it was anthologized in The Year's Best Fantasy and Horror, the nineteenth annual collection.
The titular ball room is a children's play area, with a ball pit, in an Ikea-like furniture store. The story is told through the eyes of a store security guard named John, who witnesses strange goings-on in the ball room. First a child is hurt by something under the balls. Then, another store employee quits in distress, saying that everytime she counts the children in the ball room, the numbers don't seem right – there seems to be too many kids.
On a night shift, John sees the plastic balls moving of their own accord in the ball room, then for a second sees a young girl in the small "Wendy house" at one end of the ball room. John assumes a girl has been left there by a parent overnight, and he calls his fellow guards as well as the police. But when they search the ball room there is no-one there.
Lastly, another child is badly hurt – she chokes on a ball which seems to have impossibly wedged in her mouth. Moments before the girl had been playing with some unseen person in the Wendy house, yet no evidence is found of a second child. The accident causes the closure of the ball room, which hurts the store's kid-friendliness, and thus hurts its sales.
A high-ranking executive, Mr. Gainsburg, from the parent corporation which owns the chain, comes to the UK and visits the store, explaining to John why the ball room is so important to the store financially. Gainsburg requests to go into the ball room alone, and John glimpses the man pulling out strange items once inside: a candle, a flask, a dark book, a little bell.
An unspecified amount of time later, the ball room is open again and the store's business is better than ever. Kids love the ball room more than ever, almost obsessively. It is, as John ponders, "where they want to stay".