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It's fine with me. They are broadcasting the signal, your daughter isn't piggybacking, so there isn't any harm being done. As you point out, a lot of people assume wardriving and piggybacking are the same thing, but they aren't. It isn't as if she is hoovering up private data, a la Google driving around. She isn't using any one's broadband, so there is no harm whatsoever. Mad Men won't stutter on anyone's Netflix because of a little girl riding a bike around with a Nintendo DS. Plus, there are actually a couple of people in my neighborhood that intentionally leave open WiFi for anyone to use, so I know they wouldn't mind. I'd let her enjoy her game and not give it a second thought.