The diagnostic yield of continuous electrocardiographic (ECG) monitoring in children for periods longer than a Holter monitor is unclear. The aim of this study was to characterize diagnostic yield, arrhythmia type, and time to first arrhythmia using a clinical repository of national ambulatory ECG data in children. A cross-sectional study was performed in 3,209 consecutive children receiving a 14-day adhesive patch monitor (Zio Patch) for clinical indications from January 2011 to December 2013. Of the 3,209 children (56% female, mean age 12.5 ± 4.4 years, range 1 month to 17 years), 390 had arrhythmias detected, making the diagnostic yield 12.2%. Of these, 137 patients (4.3%) had arrhythmias deemed clinically significant to warrant urgent physician notification. The most frequent indications for monitoring were palpitations (n = 1,138 [35.5%]), syncope (n = 450 [14.0%]), unspecified tachycardia (n = 291 [9.1%]), supraventricular tachycardia (n = 264 [8.2%]), and chest pain (n = 261 [8.1%]). Arrhythmias were detected in 10.0% of patients with palpitations, 6.7% of patients with syncope, 14.8% of patients with tachycardia, 22.7% of patients with supraventricular tachycardia, and 6.5% of patients with chest pain. The mean times to first detected and first symptom-triggered arrhythmias were 2.7 ± 3.0 and 3.3 ± 3.3 days, respectively. Forty-four percent of first detected arrhythmias and 50.4% of the first symptom-triggered arrhythmias occurred beyond 48 hours of monitoring. In conclusion, the diagnostic yield of continuous ECG patch monitoring in children was substantial beyond 48 hours and should be considered in children who are candidates for longer term ECG monitoring.