Cornish Estate ruins is a very cool place to explore with kids! It is an easy, short and interesting walk to the unique ruins.
Located just north of Cold Spring, this hike is part of the Hudson Highlands State Park. There is a parking lot on Route 9D, right across from Little Stony Point. From the parking lot (which has port-a-potties) take the trail to the left, the Blue Blaze trail. This trail takes you directly to the ruins, from the parking lot there is a short rugged, but not difficult walk until you reach the old driveway of the mansion that is paved and flat. A lot of interesting this to check out along the way and great views of the Hudson River.
Along the walk there are a lot of interesting things to see, and for the kids to climb on,