Take a small bottle with a special cap on it for pouring out sand - I found them at my school, but if you clean out a white glue bottle and pull off part of the top to leave the inside portion, it would look the same. Poke holes in the bottom of it and push a pipe cleaner through it.
Tie this to a wooden dowel and suspend it above a large cardboard box. Place a piece of contact paper sticky surface up at the bottom of the box.
Have the children hold a small funnel on the jar. Fill it with colored sand and let it flow into the bottle.