The Cash Flow tab is the result of the inputs in Plan, so no inputs needed there. In the Plan tab, lower right, you will see the 'Cash Flow Priorities'. There you enter the details (time span, amount, etc.) of the build up phase. In the 'Income' section you can enter the withdrawal phase on your "school" dates, as cash inflow. You can add each kid their own entries for different withdrawal date span. Under the 'Expenses' tab is where you put the details of the outflow (ie. expenses) during the "school" dates.

HTH