An au pair is a woman or man from 17 to 27 years old. They go to Britain to study English and they live with an English-speaking family. They can speak English with the family all day, so they improve their English quickly. Some of them also go to English lessons in a private school in the afternoons.
The au pair receives food, a room and a small amount of money. They have to look after the children and help with housework (usually 5 hours a day, 5 days a week). They become a part of the family and sometimes they spend their free time together.
It is a good way to get to know British culture and to learn English. Why don't you think about it in five years' time?