I can't come rescue you right now, but maybe next summer. We go to the Cape every summer. My MIL and FIL have a house near Poccassett--maybe we'll plan our escape next year.
Speaking of Poccassett, I once saw a sign for handspun yarns in front of one of the houses near the market. My husband and kids were with me and well--they don't like to shop for yarn as I do. So I thought I would find it again and stop by. Couldn't find it anywhere, until the day we are off to the airport! It was too late for us to stop and again, I had a husband and kiddos!
My suggestion would be to steal a car and enjoy the Cape. Where on the Cape are you staying? On the Upper Cape, downtown Falmouth is quite charming and the have one of my favorite children's bookstores there. The Christmas Tree shops are fun. I even had to pack a box to ship my bargins home this year! If there's a game nearby, try a Cape Cod baseball game. It's good outing for the whole family. Also, Woods Hole is a simple, free excursion. Forget the fish, my kids love to clean the fish tanks with the squeegees.