A 3-month-old child presents with intermittent strider. Most likely cause is –
Laryngomalacia 

Laryngomalacia is the most common congenital laryngeal anomaly.
It is the most common cause of stridor in infants and children.
Symptoms appear in the first 2 weeks of life and increase in severity for up to 6 months.
The typical presentation is inspiratory stridor which is exacerbated by any exertion (crying, agitation, feeding), supine position, and viral infection of URT.
Stridor is due to partial collapse of a flaccid supraglottic airway during inspiration.
Laryngotracheobronchitis
Laryngomalacia
Respiratory obstruction
Foreign body aspiration