The first 4 weeks infants are obligatory nose breathers. When they experience nasal congestion, they often get obstructed and have decreased oxygenation. The larynx is structurally soft and can be compromised by constriction, extension, or flexion. The trachea is high and close to the top of the esophagus which can lead to increased risk of aspiration. Airways are small and short so a child may have frequent mucous obstruction.
Eustachian tubes are short and straight so ear problems are common.
Respiratory rates are high. Immune system is immature which increases susceptibility to infection. Intercostal muscles aren't developed until school age. Any compromise to diaphragm can cause difficulty. Ventilatory space is small and easily compromised by abdominal distention which can cause elevation of the diaphragm.