Really depends where you stay, south vs north. Great options in both, if you are doing a beach vacation vs staying inland.

Check websites like Mommy Poppins or fun new jersey for so many lists of options and events.

My personal bias, but a little more money, check out South/central Jersey for a nice beach getaway. Cape May has a 'free'(optional donation at entry) zoo that is really nice, military museum with planes nearby, wineries for the adults, nice shopping. You can drive a bit to hit Story book Land, 8 years old is right on the cusp of Story Book Land being boring so depends what he likes, obviously Six Flags has bigger rides. Diggerland If he likes anything to do with construction trucks. There is the Popcorn zoo, where you throw popcorn at animals but it is small, South Jersey also has The funny Farm which although a little muddy, the animals are all rescues and they are everywhere walking around and you can feed and pet them. Philly zoo is also very large with the Camden Aquarium there as well.

You can still drive a bit for North Jersey and NYC but if I were personally going on vacation to relax I would look further south.