Children at age 3 can begin to describe and classify objects by what they are made of and their physical properties such as color and shape. Start them out with projects exploring water.
Water can be poured from a large container to smaller containers. Red, blue and yellow colored water can be mixed in small cups or colored ice cubes melted to form new colors. Objects can be tested to see if they sink or float. Fill a small tub with water and provide a variety of objects such as keys and utensils that will sink as well as sponges, ivory soap and plastic toys that will float. Outside, have children look at their shadows and get them to realize they need light to make shadows. Continue by making shadows inside as well with a bright flashlight. They can watch their shadows move as they move to realize the shadow is created by their own motion.
Children can make classifications at this age but limit the activity to one attribute such as plant or animal, living or non-living. Use photographs or small toys to help them make their classifications and have them match photos of animals to that animal's environment. Magnetic play kits are also available where children can put animals into the proper habitats.
They can explore the human body by looking at their features and matching them to their function (such as hands are for touching). Have a variety of objects for children to touch, such as a soft fabric swatch, a piece of fruit to taste, small bells to hear, a flower to see and some cinnamon or coffee to smell. Then they can compare human features to other animals such as their own nose to an elephant's trunk. Children can watch root vegetables grow by using a special planter that allows the teacher to open a panel, revealing what is happening under the soil. Ant farms are also a good observational activity.
Children love to experience new things in their environment. Pools, rocks and soil are good to explore with supervision. Children can look for different colors and shapes of rocks as well as different soil types such as sand or clay. Rock piles and sand boxes are great for digging and building land formations. A classroom weather chart is a good way to recognize types of weather and match them to a season. Make a large calendar with a pocket of small graphics of the sun, clouds, rain and partly cloudy days as well as snow and thunderstorms. One child can be a weather helper who can place the matching graphic on the calendar.