it was a 7 day summer camp.

I think that says it all.

Working these short term contracts isn't enjoyable but if you can stick it out then fingers crossed you get paid.

You shouldn't have taken the decision to swap classes. If you had a problem with the ages and resources you should've raised it before you started teaching. If the team leader then tells you sorry that's the way it is then you have two options. You can either just accept it, work the week collect your money and leave or you leave there and then before the classes begin. Don't take matters into your own hands with a situation like a 1 week position because as you just found out you are very expendable and you've just given them an excuse to get rid of you.