L.W.
Well you can see where the 4 year old got his rudeness from, huh? I would just thank your lucky stars that she and him are out. If she happens to call you again for another time, I would decline if I were you.
Some people are just incapable of making commitments. They live in a world that revolves around them don't you know?
I would get it done in writing if you could as to when a "client" needs your services. Have them confirm it back to you in writing. Set it up like a business would. Set up a rule for cancelations. They have until a certain time to cancel without a penalty of sorts. If they pull a no show, charge them or simply cross them off of your list. Unless of course they had some sort of an emergency that was beyond their control.
May not be an easy thing to do, but you have to set some rules in order to protect yourself and to avoid any misunderstanding. Also, by setting up these type of rules, you will also be screening out the unstable people hopefully. A lot of them can't play by rules.
Good luck!