Oh, there's tons to do in central NJ, depending on your boys interests. For the record, my son is 5, and he's pretty much at the end of the Chuckie Cheese infatuation, so I can't see how any 10 year old would be happy with it. But that's beside the point, I guess. And I assume you mean that you want something you can do with the boys, not something they can do without you.
The parks are a great source of low cost recreation, from biking to hiking to boating. Try the Somerset County Parks department web site. Somerset County Park Commission
. Similar, but not listed on the Somerset county site, I believe, is Deleware Raritan Canal State park. No one knows about it, but it's got some of the most fantastic hiking, horseback riding, boating & fishing you're going to find in inland NJ. Department of Environmental Protection
My son is a train fan, and he loves Northlandz. It's a place in Flemington that has like 5 or more miles of model train track wound through a series of rooms in a building that was once a warehouse, I think. You follow the tracks from room to room, up several floors, over bridges, tunnels, towns forests, etc. with trains running on all the tracks. Great place for a rainy day. Northlandz Welcome Page
. They also have some sort of doll museum, but really, it's about the trains.
Ages 8-10 are, I think, just about getting into serious roller coaster & amusement park type stuff. There are many, and someone else mentioned Bowcraft, which is fun, and one of the better of the small amusement parks. If you want to do it seriously, head a bit further south, to Jackson NJ, for a day at Six Flags Great Adventure. Six Flags Great Adventure
. A bit pricier than a place like bowcraft, but the undisputed roller coaster king.
Well, there are a few of our favorites. Hope that helps.