The answer to your question lies in the fact that the majority of employees are eighteen years and upwards. Employees' Rights do not go below this age because they are not considered to be of working age, therefore, whatever work you succeed in getting, you have no rights to pay conditions, employment conditions, or terms of employment.
The paid jobs, and the pay is poor, are newspaper rounds; either delivering for a newsagent or posting 'freebies' through the letterbox.
I'm sorry if I sound negative but I wish you all the best with your future.