Last summer our dog did the same thing-- wasn't eating much. We attributed it to the fact that it was a pretty hot summer, and he was a very fuzzy dog! He would eat, but only small bits, and then less every day. If I got canned food, then he would eat more of that. When the dog started throwing up for no reason, then we got him to the vet fast. They initially thought it was pancreatitis, but it ended up being cancer, and terminal.
I don't want to alarm you, Diane. Dogs not eating can have many, many different causes. Taking the dog to the vet is probably the best route. Have your mom try giving the dog some canned food or some other of his favorite treats, to see if he will eat anything. Also make sure she looks closely for other symptoms-- is the dog drinking a lot of water? Are his stools normal? Anything else unusual in his behavior?
Our "new" dog had a similar problem. The previous owner used to just set a bowl full of dry food out, and let the dog feed himself. Sometimes he'd eat, other times not-- owner said the dog was finicky. (I'm sure he was just bored, as Thump said.) Well, we started feeding the dog once a day, and only the right amount of food. Got a little better-- he was usually finished by morning. Now, I add just a small scoop of canned food to the dry, and mix with a little water. Our dog looks forward to "dinnertime", and will be finished within 15 minutes!
Good luck with the kid! I hope it all works out-- let us know how the vet visit goes.