Under-16s may only be employed if their employer has obtained a permit from their local education authority, and subject to strict rules on the hours that are worked. Those rules are detailed here: http://www.direct.gov.uk/en/Parents/ParentsRig hts/DG_4002945
you have to be 13 at the minium to work but then you can only do persific jobs like babysitting at 14, waiter/waiteress at 14/15 so it is quite restricted what under 16s can do for a job