Every year I take them out so my students can compete to see which team can best stack them top-to-bottom.
The tallest tower built in two minutes wins. Its a great game and they're so light that when they tumble down, no one gets hurt.
I'm always asked, "How did you get so many yogurt containers?". I shrug and say, "My wife and I eat at lot of yogurt".
Francesca and I made it for the first time last weekend. It was surprising easy. Basically, you heat milk, add a dab of yogurt, then let it sit in warm place.
We used a little cooler half-filled with hot water. The "good bacteria" grew for 12 hours inside a glass jar until it got thick with home-made yogurt!
There are plenty of recipes on the Internet.
You can also let your kids build glass jar towers but I wouldn't recommend it.