Either. Some newborns, especially premature ones, have something called "central apnea." essentially they forget to breath. The are treated with medicines and usually outgrow it. Obstructive apnea means something is blocking the airway. It is usually developed over time, and often (but not always) involves very large tonsils and adenoids or an obese neck. Either can be treated successfully.
Yes. Sleep apnea can result from anatomic obstruction in the nose (deviated septum, swollen turbinates, sinusitis, etc) or over relaxation of the smooth muscles that line the trachea (wind pipe). It's true that sleep apnea was classically though to be found only in elderly overweight men, but that's been found to not be true. Children can have osa from enlarged tonsils or adenoids. Consult a sleep doc.
Sleep apnea. Enlarged tonsils, and adenoids can play a role in sleep apnea. As one grows, allergies can cause blockage of the air ways as well as causing constricted maxilla and mandible which reduces the airways further. Trauma ( broken nose, deviated septum ) can occur as one grows. Extraction of teeth for orthodontic treatment constricts the arches and crowds the tongue and airway further.
Contributing factor. Heredity can contribute to it but mainly it is developmental if obstructive ' like allergies jaw formations tomgue size etc so there is a little overlap.