Only use Gatorade or G2 bottles for the sensory bottles they are a heavier plastic so they hold up better and keep a unison look so everything looks good. They come in different sizes you can find smaller ones for small hands if you need to.
Make sure to ALWAYS seal your bottles securely! I cannot emphasize this enough. Unless you want your bottle opened and the contents poured out. SEAL IT… with glue. Duct tape can be peeled off by a determined kiddo. Glue is much harder for them to open up.
Put 1/2 cup dirt or clay (the kind from the backyard) in the bottom of a bottle, and fill it with water. Let the children shake it up and watch the dirt settle. (Try using gravel, peat moss, clay, and different types of soil.) Collect different types of soil and make muddy bottles from them. Label the bottles so the children can compare the different types of soil
For a list of ALL my amazing DISCOVERY BOTTLE IDEAS click the link or the image below