Beginners are often taught how to align their feet by the simple expedient of laying an arrow down so that it touches the toes of their feet. Thus the “toe line” is born. Initially we want their toe line to point to a spot directly under the target center they are trying to hit and we call this the “square or even stance.”

The arrow is placed on the floor/ground pointed to the target. Then the toes are placed up against that line, one foot at a time.
After this point little is said about the archer’s foot position until much later when we introduce open or closed stances. (Open stances are preferred for mysterious reasons.)
However, if your archer flares, say, their front foot out a bit more than their back foot, then align their toes to the target line, their body will be a closed position. Conversely, if their rear foot is flared a bit more than the front, then their body will be in an open position. And young archers are oh, so flexible and can get into some fairly extreme body positions, all based upon inconsistent foot flaring.
Sometimes we forget that the stance exists to get our upper body into a repeatable, stable position.
Coaches would be better off to pay attention to their student’s heel lines than their toe lines. The heel line doesn’t depend so much on how flared the archer’s toes are. Or we need to have our students control their foot flares as well as their foot positions. Since young people often have, shall we say, “variable posture,” we need them to attend to this. If this seems to be an issue, maybe place “foot flare” on their shot sequence list.
Is this getting a bit too picky? Here I am addressing serious archery students. You can answer this question for yourself with a little research. The next time you are able to attend a youth archery tournament, watch a couple of those archers feet. See if their stance is repeatable or variable. Pay attention to how the feet are flared. If you want to get serious, set up a camera with a telephoto lens and zoom in on the kid’s feet. Take photos of their feet over several shots, preferable several ends. Compare the photos for foot position. If you end up seeing what I saw, you can use the photos to show your students that this applies to them.
If your students are still skeptical, do the Natural Stance drill with them. They will soon see that their body has a mind of its own as to how it will be oriented in space.
And, if it turns out that “all is well” with many of your students, you will have taught them something about the level of attention to detail that one needs to excel.
Addendum Some have noted that since the arrow is placed pointing tot he center of the target, the archers end up standing to the left or right of the target (depending on handedness) and may be shooting at an angle. This might be the case but it is not. Don’t forget where the bow is. It is hanging in space in front of us. Which means we need to stand to one side so that the arrow line can be in a vertical plane with the center of the target. Standing slightly to the side of the target lane allows the archer’s arrows to be above the target line, which they must be if they want to hit target center.
Second Addendum The phrase “to toe the line” did not come from target archery, but most likely from the military where sailors and soldiers that to “lie up” with the toes upon a line. Many people think this began in the days of wooden ships as the sailors were usually barefoot and the deck boards made handy lines.