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.
Shampoo and Baby Oil
Add Shampoo and Baby oil. I added some florescent water color paint so that the kids could see the color mix and separate
After awhile it separates even more to several different layers
For a list of ALL my amazing DISCOVERY BOTTLE IDEAS click the link or the image below