The equipment can be as simple as a mason jar. You can use a blender or mixer as well.
This is a fun project for kids. They can see cream turn into butter.  You can use cow or goat milk. We use goat milk which requires us to use a cream separator.
You don’t have to have a cream separator. You can allow the goat milk to sit in the refrigerator and after some time the cream will naturally rise. I don’t prefer this because I think it gives the butter a stronger, ripe taste.
If you don’t have goats and you want to make butter you can always buy cream at the store.
For the jar method you can use any size of jar. I wouldn’t fill the jar more than half way. Overfilling will not allow enough room for agitation.  For little kids I would recommend a baby food jar or a small canning jar. Use something that will fit comfortable in their hands.
The temperature of the cream should be about 55° for goat milk and 60° for cow milk.
Put the lid on your jar and shake back and forth. If can take anywhere from 7 minutes to 30 depending on how big your jar is and how much you have in the jar.
You will see a mass forming in the jar and will feel the butter falling back and forth. There will still be liquid in the jar. This is buttermilk, which you will drain off.
After draining the buttermilk off run cold water and rinse the butter inside your jar with cold water until the water pours out clear.
Drain the butter. Put a plate and use a spoon to work the rest of the liquid out of the butter. You don’t want to leave liquid in the butter or it will cause it to spoil.
If you want salted butter you can add salt as you are working the rest of the liquid out.
Refrigerate or freeze.
If you use a mixer make sure you put a splash guard over the mixer and a towel. You will need to whip the cream which will come to a whip cream stage but keep going until it forms butter than you rinse and drain and work the liquid out just the same as the jar method.