Fairly large dog to walk for a young child. My 7 year old son would not be able to walk our little apso lapso very far before getting frustrated and I certainly wouldn't let him walk him alone. I can't imagine him walking a dog the size of Van Dam's alone (unless someone refered me to wrong picture of dog.)
You are probably imagining a 7 year old with a collar on the dog holding onto the leash and this great big dog dragging her/him.
Now imagine a dog walking freely with a child following it. ;-)
A Weimerimer isn't really that big of a dog. Maybe tall, but thin and lanky and I understand theirs was still young.