There isn't a lot going on in Punta Cana (which is kind of the point) but if you get really restless and you want to experience something really cool, consider visiting Manati Park and swimming with dolphins!
This is a once in a lifetime experience you don't want to miss. You should remember a couple of things as you plan. You do need to make a reservation to swim with the dolphins, no matter where you choose to do it, so don't get left out at the last minute. Also, don't forget a waterproof camera!! Follow instructions carefully, and enjoy!
Manati park also has a variety of cultural activities specific to the Dominican Republic and a ton of animals and activities to enjoy.
If you have kids, this will be a great distraction. Don't forget plenty of suncreen and water though, or you'll have some cranky campers on your hands.