S.G.
I know what you mean. I realized that my husband and were falling into a sort of "quid pro quo" situation with the kids. "If you're good at the store, maybe you'll get a treat." "If you leave the playground without a fuss, you can watch a cartoon at home." etc. It was getting ridiculous because the kids started thinking they only HAD to do thing to get a reward. So...
first, we took away all their toys. All. Their. Toys. We left them their books. We have told them that they have to consistenly do three things to start earning their toys back:
1. Don't fight with each other.
2. Do as you are told, promptly and cheerfully (to avoid the moping "Whyyyyy do Iiiiiii have to do aaaaaaall these choooooores.")
3. Accept what you are given without asking for more (because my son in particular is great at taking a mile if given an inch.)
We have told them basically that if they ask for a toy back, or a treat, or to watch tv, or whatever, BEFORE they have consistently demonstrated the behaviors that we want, then they are out of luck.
This is being done in a firm but loving way. We are not trying to be mean, but rather we are trying to raise good humans who are not spoiled, entitled brat faces that can't hear "no."
Oddly, the kids respond very well to more "strictness" from us.
My suggestion is to sit them down...tonight!! And explain that there is a new sheriff in town, named Mommy. Tell them that the prize box at school is a special SCHOOL thing and is not how it's going to be at home. At home, you will have certain expectations. Make them perfectly clear and be prepared to repeat and repeat and repeat them again. And tell them that if they want to know what they are going to get, or what will you buy them, the answer is automatically "nothing."
Good luck.