Kids who love nature should consider a science fair project that involves plants or animals.
A fun project that focuses on creature preference asks the simple question of "which do they prefer?" This project looks at creatures and what their food preferences are. For instance, the project seeks to find if ants prefer to eat maple syrup or orange juice. The student merely has to observe ants, in a container or in nature, as they are offered maple syrup and orange juice and answer the question of whether they flock to one particular food.
If the student prefers plants, she may compare flower growth relative to different nutrients or additions. The student takes two separately-potted roses and feeds one rose water while the other receives water and nutrients. The student records which flower grows faster, and which one blooms sooner.
For a child who is drawn to substances and how those substances react with others, chemistry is the best science fair topic. Ice is a fun and easy way for elementary students to observe the changing properties of water. Set up an experiment to see long it takes ice to melt at various temperatures or in different settings.
Students creating a chemistry science fair project might also look at food and its spoilage. Check to see if light makes food spoil faster, then repeat the experiment with heat or water. Any or all of these variables can be included in a project.
Physics lovers tend to be drawn toward movement and energy. A classic physics science fair project simply looks at the speed at which objects fall. The student takes several objects and hypothesizes which will hit the ground first when dropped from a certain height or which will have a larger impact on the surface it hits. This project would be considering Newton's Second Law of Motion, which is force equals mass multiplied by acceleration. The student can test for any aspect of the equation by changing the objects used or adding acceleration by throwing one item and dropping another from a certain height.
A student could also test the strength of different fabrics by applying equal force to each and seeing if one fabric breaks sooner. Strength of wood, metals, and plastic can also be tested.
Young children often have a fascination with space. Everything from astronauts to planets piques their interests. Children who have access to play dough or can papier-mache will be able to easily make models of the galaxy or planets. Students may also create a project comparing the planets, including which ones could possibly support life and why.