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.
Take four or five bottles and add different amounts of water in each one, from empty to full. Mix the bottles up, then let the children put them in order from empty to full.
For a list of ALL my amazing DISCOVERY BOTTLE IDEAS click the link or the image below