Just to clarify, Canobie Lake Park is in Salem New Hampshire, not Salem MA!
It's about an hour or so north.
Salem MA has a neat little waterfront park callled Salem Willows. It has an original antique hand carved wooden carousel, a little boat ride for tiny kids, a beach, harbor cruises, and a couple of video/ski ball arcades. It's just a little place, of the beaten track. They also have homemade ice cream, salt water taffy and fresh popcorn, as well as a crazy only-found-here specialty called chop suey sandwiches. For around a dollar you get a hamburger roll, wrapped in paper, filled with onions, bean sprouts, celery and tiny bits of chicken in a very plain cornstarch thickened sauce. Sounds kind of yucky, but we grew up with them, so I still get one when we go.
I love taking the kids for an afternoon of fun.
If you're going to Gloucester, the Causeway restaurant has excellent seafood and portuguese food. It's not far from the famous Fisherman's memorial statue. Passports and the Franklin Cafe, right on Main Street are both very good, as is Turtle Alley for hand made chocolate turtles with walnuts, cashews or pecans.
For excellent seafood take a ride out of Gloucester on Rt 133 west to Essex Seafood for the best quality and lowest prices that I've found on fried Essex clams and steamed lobsters. Woodman's, on the same road, is much more famous, much more expensive and usually not as good.
Rockport is touristy but very pretty. My Place By The Sea is a very good, upscale restaurant at the end of Bearskin Neck, make a reservation, it's usually packed.
Have a great trip!