Emma has been playing with a little truck that was mine. It has a string on the front to pull it around, and she has great fun, as you can well imagine. Somehow she got the idea that when she parks it, she should tie it up, like you do a horse to a hitching post. And since she is almost-three, her idea of tying it is to wrap the cord around a bunch times. Then she gets upset it winds off.
I’m torn. My impulse is to bend down and carefully explain to her how you loop the cord over and under, showing her over and over till she gets it and can do it all by herself.
And then I think of why we have That Houshold Rule in place, the one that says not to give the kids any string or cord longer than a couple feet. (dang, the “rules of our household” article isn’t on-line. Hmph.) There’s a reason, you know. 
You know, she probably wouldn’t “get” a knot anyway, so you (and she) would end up more frustrated. I like that rule! We have a similar one, but it stems from one of my kids almost strangling as an infant.
Everything here on a string ends up as a pendulum study, then a launching study, then a first aid study.
The rules are online. Here’s the link. http://www.breadnmolasses.com/id290.html