Final answer:
To use a bag-mask device on a child who is not breathing but has a pulse, tilt their head, create a seal with the mask, and squeeze the bag every three seconds, checking regularly for breath and pulse.
Step-by-step explanation:
When a child is not breathing but has a pulse, you should administer breaths using a bag-mask device. First, ensure the airway is open by tilting the head back and lifting the chin. Place the mask on the child's face to create a seal around the nose and mouth. Then squeeze the bag to deliver breaths at a rate of one breath every three seconds or approximately 20 breaths per minute. The amount of force used should be enough to see the child's chest rise with each breath, indicating adequate ventilation. It is important to continue to check for breathing and a pulse, to ensure effective oxygenation and perfusion.