This website has what I think is close to the sound we heard. Possibly a Great Horned Owl. And here is what their hooting sounds like.
As we walked along the trail, stopping to play in new and old favorite places, we began to hear the sound of voices, children voices. And there was the blue group-hidden among the downed trees and bushes. We had to climb over and under trees to get to them. The kids were excited to find each other and I could hear the talking about the owls hooting in the trees above.
There was some stump climbing,