Younger children are most likely to be interested in something which is very hands-on, and gives results quickly. They probably won’t be interested in growing a crystal, and are probably a bit young for something like a robot building kit. Young kids will be most likely to enjoy a gross science kit, or a volcano kit. Also think about safety features when buying for younger children. Make sure they won’t eat anything they shouldn’t, or there are no small parts which could be dangerous.
If your kids are learning about genetics, you can do this edible double helix craft to show them how DNA is formed, what its different parts are, and what it looks like. The licorice will form the sides or backbone of the DNA and each color of marshmallow will represent one of the four chemical bases. Kids will be able to see that only certain chemical bases pair with each other.
My nieces are seven years old and into science. The experiments were easy and straightforward - easily read and done by the kids but adult supervision is probably a good idea. Mind blowing? Not so sure about that but very cool for the budding scientist. Perfect kit to start with. I think it's a cool way to encourage girls to love science and math. Boys will love it too - an exploding volcano! - so it really is great for the whole family. Younger kids could definitely participate with the aforementioned supervision. We LOVED it!
If you do this sidewalk constellation craft, you’ll be able to see the Big Dipper and Orion’s Belt in the daylight. On the sidewalk, have kids draw the lines of constellations (using constellation diagrams for guidance) and place stones where the stars are. You can then look at astronomy charts to see where the constellations they drew will be in the sky.
Fire is fun. Colored fire is even better. These additives are safe. They won't, in general, produce a smoke that is any better or worse for you than normal wood smoke. Depending on what you add, the ashes will have a different elemental composition from a normal wood fire, but if you're burning trash or printed material, you have a similar end result. In my opinion, this is suitable for a home fire or campfire, plus most chemicals are found around the house (even of non-chemists).
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.