If you are interested in becoming Au Pair, you should make sure you know what your duties may be in the first place. Au Pair duties may vary from family to family (as well as working hours and timetable) but it is important for you to discuss it with your future / potential host family in order to avoid misunderstandings in the future.
Some duties can be added or deleted from the Au Pair contract as long as both Au Pair and family agree, but it is important for you to make sure you are not doing more hours than what is allowed by the official program and that your tasks belong to the responsabilities of an Au Pair.
In order for you to get an idea of what Au Pairs can do and what they shouldn't do, AuPair.com offers you the following information.
What can an Au Pair do?
Play with the children
Take / pick up the children from school or any other activity
Help the children to get dressed
Help the children with their homework
Prepare light meals for the children
Keep both Au Pair's and children's room tidy
Help with light housework (ironing, vacuuming, laundry)