Use of a nonrebreathing mask or nasal cannula in a child is appropriate ONLY if:

The correct choice emphasizes the importance of ensuring that the child has an adequate tidal volume before using a nonrebreather mask or nasal cannula. Tidal volume refers to the amount of air displaced during each breath, which is crucial for effectively delivering oxygen to the child's bloodstream. If a child's tidal volume is adequate, it indicates that they are capable of sufficient ventilation, thus making it appropriate to use these devices to provide supplemental oxygen.

Using a nonrebreathing mask or nasal cannula on a child with inadequate tidal volume could lead to insufficient oxygenation, as the device relies on the child's ability to breathe effectively and take in enough air. Therefore, confirming adequate tidal volume is a critical step before employing these respiratory support methods.