The best craft for demonstrating the diamond shape is making a kite. Regardless of size, the materials and instruction are the same. This is a tangible craft children will enjoy and identify with when they make the connection to shape. Overlapping paper diamonds to make a crown is another creative way to give a child an example of what diamonds can do.
Simple songs with repetitive lyrics are very effective for conveying information. Does Conjunction Junction ring a bell? Songs about the diamond shape can be found at any preschool resource or you can simply make up your own. The tune needs to be simple and already known (i.e. Clementine, Twinkle Twinkle Little Star). The lyrics also need to be simple and to repeat within the song. Include important information like the number of sides and points. Including a word picture like "kite" is also helpful.
Ask your children to look for diamond shapes in their everyday environment. You can reward them for each one found or make it a competition between the children to find the most. This will stimulate the children's awareness of immediate surroundings and help to connect the diamond shape to the world around them. This is also an activity that can be performed at a park or in a grocery store.
Games are also entertaining and can be used as a learning tool. Cut a large diamond (each side at least 4 inches long) out of poster board. Then cut the diamond itself into 3 to 5 jigsaw pieces and let your child put it back together. Using a standard playing card deck can also be handy. Ask the child to sort out all the diamond cards, lay them out in numerical order and count the total number of diamonds on the cards.