As a professional childminder you will probably be the only person working in your business. If this is the case, you will not have to operate Pay As You Earn (PAYE) - so enter zero in this part of the cash flow projection.
If you do anticipate that your business will employ anyone then you will have to operate Pay As You Earn (PAYE) and deduct tax from their weekly/monthly wages. Every month (or in some cases every quarter) you will pay this amount to HM Revenue & Customs (HMRC), together with the Employee and Employer National Insurance Contributions (NICs). Be sure to make your payment before the monthly deadline - the amount of time you'll need to allow will depend on how you choose to pay. You will need to submit your payroll information to HMRC online 'in real time' on or before the day when you pay your employees.
Information about all aspects of PAYE, including guidance for new employers and useful tools, is available on the Gov.uk website.
Most employers who pay Class 1 National Insurance Contributions on their employees' (or directors') wages can claim the Employment Allowance, which reduces the amount they pay each year by up to £3,000. Note, however, that a company where the director is the only employee can't claim the allowance. You can find out more about the Employment Allowance on the Gov.uk website.