In Britain you can baby-sit at any age while in Northern Ireland you have to be at least 13 years of age. However, if the child you’re babysitting is thought to be at risk because it is not being looked after properly, the child's parents could be prosecuted.
2 Additional Answers
In the UK, there is no legal minimum age for babysitters but the NSPCC and Children?s legal Centre prefer having babysitters over the age of 16 years. There are no recommended qualifications for babysitters but one who is competent in first aid has an added advantage.
You can baby sit at any age whether paid or not. However, the legal guardians of the child should ensure the babysitter is responsible and well suited to take care of their child to avoid prosecution.