There are no beachfront campgrounds in NJ. However, we love Seashore Campsites in Cape May--which is a short drive to the beach.
Seashore has a great pool, a swimming lake, multiple playgrounds, and pretty much all of the amenities that you could think of.
Cape May is also a truly beautiful town. Lots to do and see and great food!
Here is a link to our last post about Cape May from last fall--there are pictures of the campground etc...