I made Butter in a Jar back when I was a kid as a youth activity. It was very easy and just took some time.
Heavy whipping Cream – any amount 6 cups makes about 1 pound of butter
1/2 teaspoon per pound of butter- optional, used for preserving butter
Jar with lid, any size, baby food jars are great for kids to make it with.
Some people like to put a clean marble in the jar and when the marble gets quite you know its starting to thicken. Just don’t forget to remove the marble when you are done,
Have the children shake the jar. A figure-eight motion seems to work best, but let your kids go wild (not so much, if the jar is glass). If you have a plastic container with a tight lid, you can even roll it back and forth.
Pour Heavy Whipping Cream into jars no more then 3/4 the way full. It is best to leave room for the shaking and turning action. Next begin shaking! And Shake and Shake. Some music to shake too makes it fun for the kids and helps pass time. Something with a fun and quick beat. The best way I figured to shake the jar was to hold it length wise in my hands with the lid in my palms and the base of the jar wedge in my forearms.
It takes about 5 minutes before you notice a thickening forming in the jar. This heaviness is the beginning of the fat changing and sticking together. At this point you really just have a thick whip cream in the jar. Keep shaking.
As another 5-10 minutes pass you will notice the jar filling with the foamy cream. It feels as if there is no room in the jar as the thick Heavy Cream is aerated even more with the shaking, but keep shaking. It will look like this: