A 3-month-old child presents with intermittent strider. Most likely cause is –
Laryngotracheobronchitis
Laryngomalacia
Respiratory obstruction
Foreign body aspiration
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.