Final answer:
A bolster or block can be used under the forehead in child's pose when it cannot reach the ground, supporting the body and preventing strain.
Step-by-step explanation:
In child's pose, if the forehead cannot reach the ground, you can place a folded blanket or a bolster under it. This allows for a comfortable position while maintaining the integrity of the pose. Props like a block, bolster, or blanket are commonly used in yoga to accommodate different flexibility levels and to support the body, ensuring proper alignment and preventing strain.