This crafty project can be a lot of fun to make, and it can teach your kids a little history lesson at the same time. The good news is all you need is two plastic bottles of equal size, a two-hole button, some clear tape and colored sand. Take the lids from the bottles and find a two-hole button that fits tight in the mouth of the bottle. Add your colored sand in one bottle, and then place the button in the opening. Then get the other empty bottle and place it on top and tape it all together, making sure you have a tight seal. Now your hourglass is ready to use. Measure out the length of time it takes to completely empty the sand from one bottle to the other and explain to your kids that this was how early timers worked.