You are not expecting too much. The kids will adapt just fine. They may not like it but that is life. I refuse to use tangible rewards. Bribary is only short term. I hate it. Every year my students ask "what do we get if we do the assignment?"
Since when did education and behavior expectations turn into Happy Meals from McDonalds? Why does there need to be a prize for doing what you know you should do anyway?
They will get over it, you just have to be strong and set up the boundries right away. Be firm, and lay down the law.