There is no National Insurance contributions (NICs) liability for employees aged under 16.
If one of your employees reaches 16, and your payments to them equal or exceed the Lower Earnings Limit, you will have to start working out employer's and employee's National Insurance contributions (NICs) based on their gross pay and recording the details on form P11 or an equivalent employee payroll record (either electronic or paper).
HMRC has produced a flowchart you can use to identify the appropriate NICs category letter (also known as table letter) to use for these calculations - use the link below.
You should deduct PAYE tax regardless of an employee's age, once their earnings exceed their personal allowance.
Download employer helpbook E12: PAYE and NICs rates and limits (PDF 214K)