When I was in high school, I had this great teacher - Mr. Carlson - who taught a one year course, Field Biology. It had lots of benefits, and field trips, including backpacking trips and after school hikes and trips to check out elephant seals and various other kinds of nature studying events. It became so popular in our school that a second year of curriculum was developed, brilliantly named Field Biology II, with more of these kinds of activities and studies.
At that time I discovered birdwatching, or more accurately for me, bird checking. We were given a long list of birds that at that time were known to be in California, either for the year or as part of their migratory trek, and we tried to see as many as we could through the process of all these field trips, and indicate what we saw. What it did for most of us was take us from noticing there were birds all around, to noticing what kinds of birds were around, and what that meant about the ecosystem as far as food and predators and water and botany was concerned.
I've had a trusty Audubon Field Guide to Birds ever since, and it's rubbed off on the kids. I get excited about seeing new types of birds in our neighborhood, and I'll consult the book, and the kids and I will figure it out, and one of them will excitedly tell Mom what we saw at the first chance they get. This usually opens up a discussion as to why they might be around here when we've not seen them much if at all before. Sometimes birds show up around here and are common for a season or two, but then disappear and aren't nearly as visible for a while. This happened a few years ago with Baltimore Orioles - Cal Ripken drove up - scratch that, stupid joke - one summer we saw them in our yard all the time, which was a first, but we haven't seen much of them since. Sometimes they appear and stay - about 5 years ago goldfinches started showing up, and they're here every summer now. This year I've been seeing more blue jays in our part of the neighborhood. And gladly, at least for now, less crows.
Anyway, I just felt like recommending the activity. Central Pennsylvania is rich with places to bird watch, for different kinds of birds - rivers and creeks, "mountains", farmlands, and practically every suburban neighborhood. And with the richness comes the fact that birdwatching is actually very inexpensive, and flexible - you can take five minutes or 3 hours, depending on how much focus you want to give it. Binoculars and a reference for determining on the spot what bird you're actually seeing and you're set. You can build your own PA Bird Checklist to monitor with your kids here or here.