Stamp a playful canine-inspired border of cartoonish dog bones around the top portion of the walls, alluding to the penchant most dogs have for chewing on bones (whether rawhide bones or the real thing). Other uses for the dog bone motif in a kid's bedroom include making a giant white bone-shaped pillow to lay across each child's bed and accessorizing the room with whatever dog bone-shaped vintage items you can find, like a playful light-up bone lamp or a whimsical vintage painting showing a dog with a bone.
Paint a wall-size mural depicting the kids' favorite kind of dog, whether a particular dog or a beloved breed like Dalmatians or golden retrievers. If that kind of dog boasts a distinctive coat pattern, like the Dalmatian does, you could just paint the wall with a large-scale version of that pattern. Alternately, create a mural showing a dog bounding through a field of wildflowers, chasing a squirrel or just lounging contentedly with a bone. If the dog you want to show has a dark-colored coat, balance it with a brightly colored background to avoid making the kids' room gloomy.
Give the kids a space for play with a doghouse-style playhouse. If you have small children, you could actually buy a new doghouse intended for a large dog. Children often enjoy having enclosed play spaces, which can function as anything from a cave to a spaceship to a house in their imaginative games. Alternately, if you have some crafts know-how or can hire someone else who does, make a larger playhouse painted to resemble an oversize doghouse -- perhaps painted the cherry red of the home of the beloved cartoon dog Snoopy.
Craft a wooden sign for the door depicting a smiling cartoon dog along with the words "Welcome to the Doghouse." Such a sign will prepare new visitors for the dog-themed interior and set the mood of the bedroom as a place for imaginative play. Other dog motifs that could be repeated on the sign and throughout the bedroom include paw prints, dog bowls and dog tags.