When a new employee is added to the payroll it is the employers' responsibility to ensure they meet the employees’ rights and deduct the correct amount of tax from their salary. This includes any employees who are family members.
HMRC’s guidance is clear that if you hire family members you must:
It is possible to employ young people if they are 13 or over but there are special rules that govern how long they can work and what jobs they can undertake. Young workers and apprentices have different minimum wage rates from adult workers for the National Minimum Wage.
There are different rules if you take on volunteers or voluntary staff, but you as the employer are responsible for health and safety and must give inductions and proper training for the 'job' at hand.