One of the things we tried to learn when we were kids was how to draw the basic shapes. Shapes are, after all, one of the fundamental elements of art. Our lines might have been a little crooked, but I am pretty sure that, even when we were that young, we could already come out with distinguishable forms. 
Triangles were no problem. Squares were no problem. Other polygons were no problem. There was only one kind of shape that baffles even the kids of today. This was the circle.
We were taught that the circle has no sides. Instead, it was a collection of points equidistant from some center point. That sounds easy to say, but when you were a little kid with hardly a good grip, drawing a circle could be a nightmare.
I should know. I've been there. Back then, without any tools, I would create some sort of mutant polygon. Even if I had some guide, like a coin, the circles drawn were far from perfect, too.
Your kids may be having a hard time today with their circles. So try to help them and provide them with a tool that can help them draw those nasty rounded figures easily. Get them something as easy to operate as a compass.
I learned how to use one when I was a little older, but I wished I had them years prior to that because they are so easy to use! At first there's some getting used to, like with any other tool, but later on one will realize how easy they were to operate.
What is so wrong with children having compasses as their first drawing tools, anyway? I would say none.