-empty 2 liter soda bottle
-tiny bit of cooking oil
So clearly, you fill the empty bottle with a little bit of water. You can fill it as full as you like, but the fuller you fill it the heavier it gets, which makes it a little harder for little hands to pick it up. I filled it about 1/5 of the way full. I chose blue food coloring and just added a few drops, and then added a little bit of vegetable oil to give it some "bubbles." Then I added the balloon. You have to stick it in deflated, and blow it up once it's in there. Obviously it won't get very big, but it doesn't need to be. You could really put anything in there that would fit, but I thought a balloon would be fun. I contemplated putting multiple balloons in, but decided on just one for now. I can always add more.
Riley loved shaking it, turning it up and down, but most of all, she liked to roll it across the hardwood floor. She also enjoyed my spinning it for her. Hours of fun. :)
Things to keep in mind: SCREW THAT CAP ON TIGHTLY! You don't want food colored water spilling everywhere! We have a white rug so I made sure it was leak proof about 10 times before giving it to Riley. Enjoy!