Here we have 2 owners and then 2 others who fill in for us when we can't. For instance I have 3 kids and my co-owner has 1....when they are sick or have appointments we have one of our friends (the other 2) fill in for us. So there are always 2 workers here. If we can't find someone to fill in...the sick kid(s) hang out in my bedroom with one of us there checking in to see if the other needs help.
The ONLY time we ever close is 2 days a year for a "Staff Retreat" AKA Girl's Weekend.
The parents know about this when they sign up with us and it's the same days each year.