Many host families look for an au pair with a driving license because it is helpful to have an au pair who can drive when taking care of tasks such as bringing the children to various appointments and picking them up.
Even when the au pair has a driving license, it is also important that the au pair has enough driving experience to safely and confidently drive the children where they need to go.
As an au pair, you should enquire early enough if your driving licence is also valid in your host country or if you can get an international driving permit. Please ask the competent authorities.
If you would like to work as an au pair in the USA, you should in any case have a driving licence and sufficient driving experience. When you apply to one of the authorized au pair agencies in the USA, you will be asked if you have an entry in the central index of traffic offenders.