This is the EASIEST and one of the oldest science experiments out there, I chose to glam it up a bit for my toddler to play with, and to potentially learn how buoyancy works, so far it's just fun to make him dive and surface, and I have to admit, I've played with this as much, if not more than she has, my husband even wanted to make one so he could play with one too!
Step 1: Go to the fishing section
Get a fishing lure squid, bonus! Most of them glow in the dark, they are really easy to find!
Step 2: Eyedropper
Get yourself an eyedropper, this one was glass I'm sure a plastic one would work, you just may have to add a weight or something to the bottom
Step 3: Wiggle them together
pull the squid over top of the eyedropper, it may take a lot of wiggling, as the rubber eyedropper tip is a lot wider than the squid head, I found it easier to oil the squid and turn it inside out, rolling it onto the eyedropper, being sure to wash it before you put it into the water.
Step 4: Suck up some water
Squeeze the bulb of the eyedropper and get about enough water to fill just the bulb, this may take some trial and error, to get enough water that his head just comes above the surface
Step 5: Neutrally buoyant
This is what it should look like to be neutrally buoyant, prepare for awesome. (the term neutrally buoyant brought to you by my dive instructor Neil, and the letter E, for Ed, Ed owns the dive shop, Ed and Neil are good peeps.