The following is a video of fat particles milk under a microscope. Their jiggling movement is called Brownian motion. The video notwithstanding, kids will gain a much more meaningful and lasting learning experience when they view it for themselves under a microscope. For this viewing, follow directions in the text being sure to get a good focus working your way up to high power (400 or more x); use the condenser to cut down light intensity, and give attention to the tiniest particles. Please post your experience.