When Queen Victoria ruled the British Empire, it was popular to make "phantom bouquets" from skeleton-like leaves. Making skeletonized leaves is a great way to see how leaves get the water they need to grow. Mature maple or oak leaves work especially well. It's an eerie experiment and it requires patience, but if your child likes being a mad scientist in the kitchen, this is a fun way to see a leaf's framework.
Combine four cups water and one teaspoon washing soda in a stainless steel or enamel pot. Add a fresh, mature leaf. Bring to a boil and simmer for thirty minutes, then let the water cool. Lay the leaf flat on newspaper and, using the dull knife, slowly scrape away the fleshy surface from both sides of the leaf, leaving the veins. If your child works carefully, what remains is a beautiful, but spooky-looking, leaf and you can see how intricate a leaf really is. Trees drink water through their roots, then carry it (along with dissolved minerals) through their veins to every part of each leaf. Once sunlight and chlorophyll have reacted with the water and carbon dioxide (from the air) to make sugar, the veins carry it to wherever the tree needs food.
If your child did a near-perfect job of scraping the surface off the leaf, he might like to make an "angel wing" to use in a dried flower arrangement. Bleach the skeletonized leaf in a solution of two tablespoons bleach and one litre of water for about an hour. Remove the leaf and rinse it with water. Gently wipe it dry with a soft cloth.
Place it between two pieces of paper towel and press between the pages of an old phone book. If you're pressing more than one leaf, make sure you have at least one cm of pages between each leaf. Put the phone book in a warm, dry place with good air circulation. Avoid damp floors. Add weights. (Heavy books are good.) Check the leaf after two or three days. Fold a length of florist wire in half and place next to the stem. Wrap the wire and stem with white floral tape.