Ya ~ I choose my closures based on time that works with my spouses work schedule ~ clients have to work around that.

One of the things I do at the beginning of summer and in November / December newsletter is put something in the my newsletter along the lines of ....

"I realize that this is the season for spending time with family and traveling to visit relatives ~ if your family plans on taking time off this season in addition to my normal closures of XYZ if you could give the program as much notice as possible to help with planning meals, program activities and field trips that would be greatly appreciated'."
However my clients do not get a 'payment credit' for taking additional time off so there is no 'time frame' they have to let me know by ~ they still have to pay me full fees regardless ..... so they are basically doing me a favor in letting me know ahead of time if they will be gone otherwise they have until 9am of the morning 'of care' to let me know of an absence that day.

I personally do not like to 'share' what i might have planned specially with low ratios because I find than some clients read or hear about it prior and end up choosing to send their kids anyway cause they do not want them to miss the 'trip to the farm' or whatever special thing you might try if you thought you only had 3 kids instead of a full house and so forth