We stayed at Mt Desert Narrows and found that there was a shuttle that stopped at most of the campgrounds and would take campers (for free) into Bar Harbor.
The ages of kids you are talking about are way beyond "playground" stuff. This age of kids congregate around the wifi hotspot.
This may sound cynical BUT (in this day and age) the place I saw most teens was at the closest wifi access with their faces in their phones. SERIOUSLY
Where ever you end up going, if you want a teen to enjoy themselves make sure there is wifi/Data access!