Not sure about VIC but in NSW family day carers can charge for a public holiday even when they don't provide care but only if they are available to provide care the day before and the day after a public holiday. If they do provide care they have the right to charge a higher rate for the child/ren using care. Remembering that no fees are charged if care is unavailable (ie, sickness or holidays) so that bonus day can be very worthwhile for a carer financially. After all most working parents are paid for public holidays {if you aren't working, can you change your care day (the only public holiday you might then get is christmas/boxing day)} if paying is a problem. It is also a personal decision if the carer charges this day or not.
New changes are coming in, with each child receiving 42 days absences each financial year, this will now include public holidays, absences days and if you use your 42 days prior to all the public holidays, you will be paying full fees (without subsidy) on any other absences - including public holidays - ask your carer about these changes.