Wow as you can tell Jenn from the replies it is totally a personal decision and there is no right or wrong answer. What I would do if you are still unsure is call the other providers in your area and ask them what their policy is (do let them know you are a provider I do not like when another provider calls pretending to be a parent looking for information it is better to be honest and who knows you might hit it off and do playdates together!) then look over your list and see what the majority says.
I too do not charge parents when I am not providing the service. I do charge parents half fees to hold their child's spot when they are on vacation so if they book the same holidays as me then they win if not then it will cost them.
Being self employed does not mean we are entitled to the same purks as parents working for an employer but we can make our own policies and then it is just finding the right families that will accept them.
Good luck Jenn with your decision.