Hi Sootie~~
I can answer this! Butter is the byproduct of "churning" the milk. The agitation of the milk causes the fat globules to separate from the fluid part of the milk. When the process is finished you have butter and whey. The whey is where all your calcium and protein went.
Here's a fun experiment you can do with your daughter. Get a pint of heavy cream and place it in a quart sized mason jar. Have your daughter start shaking it very gently. After about half and hour to an hour you should have butter and whey!
Use a spoon to mold the butter into a ball, then drain off the whey.
Hope that helped.
Mamacita