Our "garden"

I am getting a bit worried it seems our plants are dying. We had a beautiful flower one day on the cucumber and the next day it was dying. I have not done a thing different to these plants! The only thing I can think is being outside after all this time inside is not a good choice for them. I don't get how I am suppose to harden them by sitting in the shade for a few hours if they are going to die. I do not want these plants inside all summer long! Some learning experience for the kids when I don't even know what's going on. If anyone out there knows what may be wrong PLEASE help!