In this video, Brittany describes how to create your own Sensory or "Calm Down" bottles at home.
These are great for children, not only to keep them busy and entertained, but can also alleviate anxiety. --Watching the contents descending and swirling can not only memorize them, but can calm their breathing and help regulate themselves and their emotions.
In addition, while the children manipulate the bottles by rotating, shaking, etc., they are simultaneously improving their fine-motor skills and concentration/focus.
These bottles are also great to build on science knowledge such as cause and effect, since they can see how different movements of each bottle cause different sounds and effects within the bottles.