Right at the start of the book, Little Bee tells us how she wishes she were a British pound coin instead of an African girl: then, at least people would be glad to see her coming. She'd also be able to visit people in their homes, where she'd presumably always be guaranteed a warm welcome. Or she could visit the man at the local conner shop, in return for which her weekend companion could receive a cinnamon bun and a can of Coca-Cola. It would be like a lovers' weekend in which Little Bee, in the guise of a pound coin, would briefly enjoy happiness with someone who cared for her.
What the opening paragraph of the story tells us is that Little Bee, even at such a young age, is acutely aware of the power of money. As she goes on to tell us, a pound coin can go anywhere—across oceans and deserts, far away from the war that blights her homeland, with its sound of gunfire and the bitter smell of burning thatch. A pound coin can also disguise itself as power and property, things that Little Bee, like many children in her situation, patently lacks.
For Little Bee, the humble pound coin stands as a symbol for all the things that would make her life safer, happier, and more stable.