Employment law states that a young person must be 13 or older to start work. There are restrictions on what kind of work they can do, how much they do, and when they are allowed to work.
One of the main hurdles that you will need to overcome in employing someone of school age, is obtaining an employment permit from your local council. This is a pretty straight forward process and you should find a link on your council’s website taking you to the relevant form that you need to fill out. This will be completed by you as the employer, but the young person will most likely need to sign it too.
From a payroll perspective you don’t need to provide payslips, assuming they earn below a certain level, but we would suggest you process their wages through payroll. This is so there are records to support the payments should HMRC call in! This is especially important if you are employing your own child as HMRC could question the validity of the payments in relation to your Corporation Tax deductions.
One final point to consider is the rate of pay, which will have to comply with minimum wage legislation. That said, you can pay more than this, but it should still be at a market rate that considers the age and skill set of the young person. Again, if this is in regards to your own child, HMRC could deem that you are paying above market rate for your benefit and therefore may apply income shifting legislation, which will effectively shift the income onto you – where you will become liable for the resulting tax.
For more information see https://www.gov.uk/child-employment/restrictions-on-child-employment.