Have you ever gone into a cave and seen huge stalactites hanging from the top of the cave? Stalactites are formed by dripping water. The water is filled with particles which slowly accumulate and harden over the years, forming stalactites. You can recreate that process with this stalactite experiment. By mixing a baking soda solution, dipping a piece of wool yarn in the jar and running it to another jar, you’ll be able to observe baking soda particles forming and hardening along the yarn, similar to how stalactites grow.
This blood model experiment is a great way to get kids to visual what their blood looks like and how complicated it really is. Each ingredient represents a different component of blood (plasma, platelets, red blood cells, etc.), so you just add a certain amount of each to the jar, swirl it around a bit, and you have a model of what your blood looks like.

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?
If you’ve ever wondered why someone can measure and pour ingredients into a bowl, mix them up, and then bake the batter in the oven to make a cake, you’ve thought about science. The process of mixing certain ingredients together and adding heat causes the ingredients to react and change. For example, baking powder or baking soda in a cake recipe will react with acidic or wet things in the batter to puff it up and make the cake light and fluffy. Scientists tested these reactions so many times that they learned what would happen every time. This is called experimentation, and you can do it, too.