Hi, welcome to the forum, same as adults in most aspects, to know whether child is suffering from air hunger look for
history which includes
+ Trauma
+ Change in voice
+ onset of gagging or choking
physical findings include-
+ Restlessness, anxiety, or combativeness suggest hypoxia
+Position of comfort- attains specific position
+Nasal flaring (exaggerated opening of the nostrils)
+Abdominal breathing
+Abdominal sounds
Take care and regards.
Babies are obligated nose breathers, due to feedings, and pacifiers. If they have a stuffy nose this makes it hard for them. You can tell if your infant is having trouble breathing, the first thing you want to check their color, babies loose there color quickly, check their hands and feet to make sure they are pink if caucasian. Check the nose, the nares will flare when they have trouble breathing, then they have retractions, this is when you can see each rib when they take a breath, they suck in real hard. If they hare having these issues take the baby to the ER asap.
Watch their chest and neck muscles. If they are using those muscles to breathe, get them to a hospital ASAP. The muscles retract showing the underliing structure.
Really, if you are in doubt, don't risk it. Go ahead and have them checked out.