Six Flags Great Adventure, New Jersey (Side-trip to Pennsylvania)
We took this 6 hour road trip when our son was not-quite-four and in the midst of potty training! However, it was fun. We stopped to 'go potty' at every rest area on the highway!
We stayed at a national budget-oriented chain hotel, that offered a package plan, and free continental breakfast, and which had an indoor pool. There was also an Appleby's restaurant, and a Cracker Barrel restaurant located conveniently in the hotel's lot.
Our son loved the self-driven safari trip, especially the very funny (and somewhat obnoxious) monkeys. Put simply, the monkeys really appealed to our potty-training pre-schooler - enough said!
In the amusement park, there were plenty of rides in the kiddie area for our son, as well as attractions we could visit as a family. One piece of advice - if you are going to attend one of the outdoor shows, be sure to load up on sunscreen first! There is not a lot of shade at this park, so sunscreen is a good idea anyway.
As a side trip, we drove to Pennsylvania one day, and visited the Crayola Factory and Sesame Place. The Crayola Factory was fun and informative. We got to see how crayons are made! The area in which this is located is a bit run-down, so we did not spend any time in the area aside from the museum itself.
Sesame Place was wonderful! We could easily have spent a full day there, or perhaps even a couple of days. I highly recommend it for families with young children, or with a range of age-groups. There is really something for everyone - water parks, water slides, fountain pools, a 'kiddie' roller coaster that is really quite exciting, Sesame Street parades, and various climbing and motor activities for kids of all ages.