Interesting post... could it be that the OP does too much with her kids? That they cannot figure out how to entertain themselves?
I hardly spend any money on my kids in the summer. I work part-time and they are on their own while I'm at work. They ride their bikes everywhere and pack a snack in their bag. I don't ever give them cash as everything is either prepaid or free. They have a waterpark pass, a bowling card (2 games per day including shoes), a YMCA membership, a library card, and are in a youth golf league.
I've NEVER heard them say they are bored or there is nothing to do.
I was thinking that the OP's kids complain they are bored because the OP is so good about finding fun things for them to do! Not a criticism but maybe its time the kids were expected to keep themselves occupied and like others have said, had an entertainment budget and when its gone, its gone.