Sleep apnea is a true breathing obstruction, which requires the sleeper to awaken to begin breathing again. A child with sleep apnea wakes up many times a night to regain breathing.

These periods of apnea are characterized by loud snoring followed by periods of silence that can last 10 seconds or more. Eventually, the lack of oxygen (O2) and an increase in carbon dioxide (CO2) are the signal to wake up, forcing the airway to open with a loud snort or gasping sound when breathing resumes. Then, snoring starts all over again. This pattern generally happens several times a night.
The immediate effect of sleep apnea is that the snorer must sleep lightly and keep his muscles tense in order to keep the airflow to the lungs.
After many years with this disorder, elevated blood pressure in the pulmonary system and right side heart enlargement may occur.
Sleep apnea in children has been linked to growth problems, ADHD, learning difficulties, and sudden death. Most children who snore do NOT have apnea, but a polisomnography (sleep study) is the only reliable way to tell for sure.