I do a monthly newsletter, the same as michelle. I put in reminders about clothing, birthdays, closures, what ever we are working on that month, new or leaving people. Sometimes if there is a specific event within the community geared towards kids that I think the children/parents may want to attend, I will put info in about that (example is the Touch a Truck event).
I also include a monthly calendar on the backside of the newsletter with any important days we are doing. Example is today is Pajama Day, so that would be on the calendar. I only do a few events like this a month, but it is a reminder for the parents.
I only have 4 dck's at the moment and while some of my parents ignore it (they never participate) I do it for the parents that do, as they seem to enjoy it.