Go to Billing --> Billing Settings and scroll down to "Billing Cycle" to enable the Weekly or Monthly Billing Cycle. 

Choose "make default" for the billing cycle that the matches the majority of your families. 

If a child is already assigned a charge and the billing cycle needs to be changed, go to Family Billing, click the child's name, choose Family Settings and use the "Edit Charge" button to set the billing cycle.

Did this answer your question?