I understand what you mean, but someone with a compact would have to be pretty close, as most compacts go up to about 10x max optical zoom. They'd also have to be still to get a decent photo.
So you've got someone close to you, standing still, taking photos of your children.
On the other hand, someone with, for example, a 40D and a 100-300mm zoom lens is gunna be able to be at a distance. Sure, they'll also have to be still, but you might not even see them with that kinda focal length on the camera. And to see it pointing directly at your children would set alarm bells ringing, no doubt about that. It's highly unlikely your first thought would be "Oh, I hope that guy up there amongst the tree's is getting some nice photos of my children playing
", simply not gunna happen.