In case you missed it: Pre-school move of the month explained
Use a line on the floor and encourage the gymnast to kneel with both feet along the line. Keep their hands on their hips. This will let you see the pelvis is at right angles to the line.
While their hands are on their hips so you can see the hips are at right angles to the line, ask the gymnast to push the front leg straight along the line.
The front leg should follow the line and the back lower leg should remain on the line. Push forward until the gymnast feels the stretch and hold it there for count of 10 and then try a little bit further.
If the hips start to rotate, bring the front leg back until the hips are back at right angles to the line.
Repeat the move changing legs