Before expecting a child to sit down and concentrate - ensure they have had enough physical exercise and good nutrition.
Ensure correct posture for sitting at a desk (refer to efficient working posture).
Ensure the pencil is reasonably think for small hands to grasp with ease.
Dynamic Tripod Grip - the pencil is balanced evenly between the index finger and thumb for stabilisation while allowing for movement.
There should be no noticeable tension in the wrist of fingers.