You may apply to become an au pair in the UK if you hold a passport from one or more the following countries:
Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden and Switzerland.
Candidates from Bulgaria and Romania are also able to apply, but have to fulfil extra conditions.
In addition, you may apply if you hold a passport from one of these further countries but you MUST apply for a visa under Tier 5 Youth Mobility Scheme.
Australia, New Zealand, Canada, Japan, Monaco, Republic of Korea, Taiwan
Furthermore, you must be unmarried and have no children of your own.