In addition to the items you already mentioned, you might try Indian Echo Caverns..just a few miles west.
Also, based on the ages of your children, I would bet that they'll enjoy Dutch Wonderland more than Hersheypark..While there are rides/attractions for younger children at Hersheypark, almost all of Dutch Wonderland is geared more toward pre-teens.
Lancaster County PA is also a good area for outlet shopping if you are into that (again, an adult activity if one or the other of you wants some time away from the kids and the other is willing to step up).
On Rt. 30 there is the Amish Farm with house that you can take a self guided tour. Also Good and Plenty. In the same area there is an Amish School house (look it up with the tourism info, I don't recall the name of it). In Blue Ball there is Kitchen Kettle Village, which is a shopping village of sorts, but there are also buggy ride and a small museum about the Amish. Just down the road from Kitchen Kettle is a place called Kings Homestead. Multiple buildings of Amish wooden wears as well as a fish pond that the kids can feed the fish. Worth the ride for a meal is Shady Maple, it is in East Earl near the Blue Ball area. I love their breakfast, though any meal there is great.
I know these aren't "kid" attractions, but I visited all of them as a child and took my son at the age of 3 to several of the places when we spent a long weekend in Lancaster.
Good Sam Life Members. Camping with two young children in a 2007 Pilgrim fifth wheel (278BHSS) pulled with a 2002 F350.