Making a 3D model of the Earth is a fun and useful way to teach kids about the planet and its properties. There are a variety of ways to make a 3D model that kids can make for anything from a science project to something that they can hang in their room as decoration.
Use a craft foam ball as the basis of your model. These balls can be found in a variety of sizes at most craft stores, depending on how big you want your model to be. You can paint it blue and green according to the Earth's geography. To add texture, try using green sand, sprinkling it on fresh green paint that hasn't dried.
Paper Mache Balloon
Paper mache is another way to make a 3D model of the Earth. Mix up some paper mache and use a blown up balloon to hold the model. Place layers of paper mache over the balloon and let it dry. You can then paint the dried globe to look like Earth. Another idea for texture is to paint the paper mache globe blue, and green, and glue on blue saran wrap over the blue areas to mimic moving water.
Old Sports Balls
If you've got old sports equipment, like a basketball or soccer ball, recycle it into a model of the Earth. Use acrylic latex paint for painting these balls, as some paints like oil-based ones will not dry properly to their surface. Since these balls have rather thick surfaces, you can even try adhering bits of green modelling clay to them to represent raised land.