A Year Ago I Put Saltwater in a Jar [video]
I live near a fresh-water lake in the middle of Europe, and decided to do this experiment with my kids a few years back .. we took a jar, scooped up some water, threw a couple small bits of algae in, and took it back to our kitchen, where we watched it daily for months.It was extraordinary to see things growing right away .. the kids loved getting up and checking on 'the critters and the goop', as we called it.Our patience was rewarded when I spotted a tiny hydra had attached itself to the side of the jar ..https://en.wikipedia.org/wiki/Hydra_(genus)We watched it grow and grew, going from near-microscopic to the size of one of the kids finger nails, turning a deep and vibrant red as it aged.There were lots of other things too, which we never got quite around to naming .. freshwater shrimps, a couple of tiny fish (which didn't survive a heat-wave also, alas) .. but eventually it became a murky mess, and we cleaned the jar out for other experiments.This is a really neat way to teach kids about life, in my opinion.  The next time we do it, we'll rig up a USB microscope and have it pointed into the depths - I have a feeling that my kids are going to find operating the microscope far more intriguing than any video game.  Would be grand to discover there's a microscope out there that can be remotely moved .. we may have to cannibalise a 'light following flower robot' to rig up our own "Exploratorium"™ .. ;)