Rest position is also known as Child’s Pose in Yoga. It’s a really lovely stretch as an exercise in itself, or use it as we do in class to release before we transition into another start position and exercise. It’s also gives really lovely feedback for lateral breathing practice!
The demonstrator in the clip has her knees together which gives support to the lumbar spine helping you to feel the release in that area, and if you keep your knees wide you can get deeper into the hips which stretches the glutes nicely too – so maybe try doing both.
To stretch out your side line remember that you can walk your hands in one direction and then the other.
If you find your knees struggle in the position try putting some cushions behind the knees to reduce the angle of flexion. If you still can’t comfortably do this position consider lying on your back and bringing knees to chest or lying in the foetal position.
If your arms struggle in the outstretched position consider having the palms facing in, thumbs pointing in the direction of the ceiling. If that’s still tricky, lengthen your arms down by your sides palms facing up releasing them.