It's so hard to say no!

It's so hard to say no to my kids. Well I can say it very well, but they don't listen to me when I do say it. I really have the best intentions. (Ready for the excuses?!) I am a mother of 3, an English teacher in kindergarten and grade 2, a wife, housekeeper, cook, chauffer, etc. Some days I am just so overwhelmed with everything I have to do. I am tired. More tired than I have ever been in my whole life. When it's 5 pm and I'm making supper and one of my munchkins come calling, my good intentions just fly out the window. It's easier to stick to my guns with the 2 older ones. Zach will stomp his feet, say a "No Fair!" (hey, who said life was fair!) and slam his door. Dahlia has a shriek that will shatter glass. I have to admit, I particularly enjoy how she watches herself crying in the mirror when she has a tantrum. Can you say Oscar Winner! Noah, my baby, gets away with murder!! I can't help it. That face is sooo cute, the tears are sooo real and at 4 you still can't reason with him. Or maybe you can and he knows that he has me right where he needs me...in the snack cupboard, at the computer or the official channel changer. I want to be strong, not only for myself, but also because I know that they will benefit from not always getting their own way. It's hard being a working mother. We are apart more than we are together during the week. It comes back to being stressed and tired. Is a cookie or two before dinner worth a battle or harmony? Does that make me a bad mother? What do you think?