Raw eggs, paper to wrap eggs (toilet paper, tissues, newspaper, etc.), tape, bags
Wrap several raw eggs in different materials (toilet paper, newspaper, etc.) Let your child help choose the materials and wrap the eggs. Then place each wrapped egg in a plastic bag. Now you're ready to test them to see which wrapping protects the egg from breaking. You'll definitely want to go outside for this in case some egg leaks out of the bag. If you have a balcony, that's the ideal place to drop them from, but you can also have your child stand on a step stool or even just hold her arm up as high as she can before dropping it. You can also try using different amounts of the same material. Will a little toilet paper protect the egg? How about a lot of toilet paper? You and your child can have fun with different variations of this. Just don't forget to put the egg in a bag, or you'll have a big mess to clean up!