Gather your desired quantity of cardboard boxes with closing lids (any size will do). You can choose to make blocks for all 26 letters of the alphabet or just a few letters.
Cut out pictures from old magazines that have objects in them that begin with specific letters from the alphabet. It helps to choose pictures that children can easily identify, such as an apple to represent the letter "A." Cut out three or four pictures for each letter so that you will have enough images to decorate the box.
Glue the pictures on three to four sides of the box with white craft glue. Avoid using too much glue on the back of the pictures so that they will adhere to the box in a level fashion. The remaining sides of the six-sided box will be used to display the letters.
Draw or trace the letters of the alphabet on the remaining sides of the box and color or paint, as desired.
Purchase your desired quantity of pre-made wooden blocks from a craft store, or in the crafts section of a department store.
Paint the blocks with craft paint. Choose a shade that will provide a contrasting background for the letters. For example, if you are going to paint the letters in red, choose a yellow or white background so that the letters will be easy to read.
Allow the blocks to dry according to the product instructions, and repaint two to three times more, allowing drying time after each painting.
Use alphabet stencils to draw the letters onto the blocks with a pencil or marker. Freehand the letters, if you desire. Fill in the stenciled or free-handed letters with craft paint, paint pens or markers. Use colors that will show up well on the background color of the blocks. Draw pictures or add stickers, as desired. Allow all paint to dry thoroughly.
Place the blocks on a clear, plastic drop cloth or other disposable surface and spray with a clear polyurethane spray to seal. Allow to dry according to the product instructions before use.