We made ocean in a bottle today, it was very fun. Sadly ours didn't turn out like some I found online. I think my sand was to fine and dusty because it made our water cloudy. They were sure fun to make though. Ella had fun putting in the sand, the shells and the water. After they were all done they were fun to shake.
This project can get very messy so I would suggest having a shallow plastic bin to make them in or go outside. I filled three bowls with course sand, fine sand (which I don't recommend) and small sea shells. I let Ella spoon them each in. It took a little longer with the spoons but she could do it without help. Of course that is why it was messy, because half the sand she poured did not make it into the bottle. We then filled the bottles with water, which I also let Ella do by herself while I held the bottle. I filled a large mixing bowl with water and gave her one of my measuring cups to pour the water in with. I then added a little blue food coloring, and capped the bottles. I used shiny silver duct tape to wrap around the tops so when I am not looking, later, they are not opened and spilled on to my carpet.