Measure the walls lengthwise, and cut two pieces of molding to fit each wall. (Try 1-inch-wide molding that is 3/8 inch thick.)
To create the ledge that the cards will sit on, cut lattice strips to match the length of the molding. Line up the lattice strip along the bottom of the back side of the molding, and adhere with wood glue. Clamp the pieces together; let dry.
Prime and paint the molding; let dry.
Using small finishing nails, nail the top molding to the wall, placing each nail 2 feet apart. If you're worried about splitting the thin molding, use a nail spinner: Attach it to a drill, and spin the nail into the wood; this will prevent the wood from splitting. Use a nail set to sink them slightly.
Measure up from the floor or the top of the baseboard to the bottom of the top strip of panel molding, which you've just installed. Whatever the height of the cards, subtract 1/2 inch for the distance between the top and bottom moldings. Install bottom molding.
Using a Q-tip, paint over nail holes.
Gently bend the cards to fit into the moldings.
2 pieces of molding
Lattice strips (long, thin pieces of wood that should be thinner than the molding)
Nail spinner (optional)
Alphabet cards, or flash cards, post cards, photographs, etc., of a uniform size
Paint the wall above the frieze a deeper shade than the area below to give the room a child-friendly scale. Installing an alphabet frieze is as simple as nailing up two parallel strips of panel molding: Space the strips slightly closer together than the height of the cards themselves. To insert the cards, bend them a little, and pop the ends in under the strips.