Discovery Bottles (aka Sensory Bottles) might be my very favorite thing to make for kids (and adults) to play with. I first learned about them when I was a teacher. The preschool room nextdoor had made a few and I was completely enthralled. The ones they had made were just oil and water in bottles. I say "just" but that is one of the coolest discovery bottles out there. I could hold an "oil and water bottle" for minutes on end just moving it back and forth and watching the reaction inside. There are millions of things that you can put in discovery bottles and they are not only fun but can be used to teach LOTS of concepts and (as long as you make them tamper proof) they are great for any age!
Here are five of my favorites!! It was really hard to pick just five. There will probably be a sequel to this post.