My holding fee is 50% of regular fees. I had a family pay this for 7 months. I had just moved house and reopened my daycare in a new area and wanted to only have a light load of children so I could have more time to get unpacked, organized and decorate. I new when I wanted to be at capacity so I accepted enquiries and at that time there was a huge shortage of providers in the area so parents new that if they didnt pay to secure a spot then there was a very small chance they would find a provider. There is no immediate financial benefit to holding a spot for an extended period of time only a certain amount of assurance that you have filled the spot in plenty of time but everyones circumstances change so this isnt always the case. Yes they may shaft you and by making a financial commitment you know they are more serious about the arrangement. I would add to your contract that this holding fee is not refundable as it is compensation for you losing money by holding the spot for them. If you wanted to offer the family more assurance I would perhaps give a minimum commitment time of 60 days or put in a clause that if you terminate the contract before care starts that you will refund the money but if they terminate then they lose all the money.
There are lots of ways to go about this and I dont think there is 1 way that the majority do. You have to think about your area and what you are willing to do in your business. Good Luck, I know it is a difficult decision.