I charge full fees if a family wants to hold a spot. I have had two families do this since I opened last spring, one was someone holding a spot for their baby while they sent their older child during a maternity leave. The other was for a school age spot. But here in Winnipeg there is high demand and I am licensed and accept subsidy so my spots would be worth paying to hold onto. I think supply and demand really affect how you would handle this situation.
The families were welcome to send their child if they wanted to during that time if they wanted, as it was technically their spot. But the days had to be prearranged.