Unless they hold their own insurance, your friend would be covered for his/her own liability if he/she was held legally liable for causing accidental bodily injury or property damage as a result of the work, despite the fact that he/she was paid. However, your parents would need to take separate Employers' Liability insurance, in case of injury to your friend: this cover is a legal requirement and may possibly be included under some household contents policies.

Related Links:

The Pony Club Website - Members Insurance