Since it is the breeder's obligation to warn the buyer if the pup is not structurally sound and ask a lower price because of the defect, let's talk about the other two possibilities, which are ones we can do something about. Dogs are often purchased especially for the children, and these youngsters are encouraged to take the pups for walks, to play with them and have some interaction with them.
Puppies are curious little creatures and love to investigate when they are out. A child out in public with a dog should have the animal on a leash. However, dragging the pup around teaches the pup to hate the collar, the leash, and to balance himself against the pull of the lead by "sidewinding" with the head pointed away from the handler.
Frankly, I like to use a retractable lead which is a lead that expands to 6 feet (or 12 or 16 feet depending on the size purchased) and recoils into its case as the animal runs back and forth. If I had purchased a pup for my child, I would get one of these leads for the child to use. The puppy has some freedom and learns the distance it is allowed without being dragged.
One nationally known trainer forbids dragging in her classes and suggests using squeaky toys or treats if the pup starts to hang back.
The second possibility that is easily correctable is to slow down so the dog's feet do not get in the way of each other as the dog gaits. It is essential that the dog does not get in the habit of "sidewinding" because the habit is difficult to break.
Dogs that have faulty conformation (short back etc.), or have an injury to a leg will often start gaiting normally and switch over to "sidewinding" later to ease the strain on the muscles.
Another fault for dogs is pacing (like camels or pacing horses where both legs on one side move forward at the same time), which some dogs revert to when they are tired or the muscles start to hurt. One of my old dogs paced after back surgery.|3/16/04|***