Making a borax snowflake is a crystal-growing project that is safe and easy enough for kids. You can make shapes other than snowflakes, and you can color the crystals. As a side note, if you use these as Christmas decorations and store them, the borax is a natural insecticide and will help keep your long-term storage area pest-free. If they develop a white precipitant, you can lightly rinse them (don't dissolve too much crystal). Did I mention the snowflakes sparkle really nicely?
Geode Kits – For any child who thinks rocks are boring – a kit where they can break open their own geode is a great way to change their mind. National Geographic is a great choice if this is the type of kit you are looking for. Their products include hand-picked geodes and come with safety goggles and a stand for your child to proudly display their treasures. A great choice for children aged around 6 years old and above, they’re sure to be more interested in Earth science after this experiment.