When I was a kid, there was one event I looked forward to every summer--Lakemont Park! My cousins and I would all get together, and make the 2 hour drive to Altoona, PA for the day. I would describe Lakemont as an amusement park for children 12 and under, although your older children will probably have fun too. It is filled with carnival rides, a water park, and one roller coaster, much like the "Comet" at Hershey Park. One of the best parts about the park, is that you can spend all day having fun there, for a fraction of the cost of other amusement park, or even the local fair! Regular admission is $9.95, but every Wednesday they discount tickets to $3! ($1 when I was a kid!). Not only that, but it is a pretty well kept secret, and I've never seen the park super busy. My last trip there was about 3 summers ago, and even then, if you had to wait in a line, it was usually less than 5 minutes. Many rides do not have a wait!
There are other things there that have a cost (go-carts, arcade, mini golf) but these activities are still reasonably priced. Unless reserved for the day, they also have pavilions available so you can bring your own lunch, or purchase one there. Parking at the park is also free. My daughter is still too young to enjoy Lakemont, but when she is older, it will no doubt be an annual event. My niece and nephew will be visiting this summer, and I can not wait to take them!
Check out their website, www.lakemontparkfun.com. It's a lot of fun, and I'm sure your kids would love it! If you go, you must ride the Toboggan--my personal favorite!