The laptop, which may not have been encrypted, was stolen on Oct. 18, according to the hospital. But officials did not learn of the theft until late December.
Officials said the laptop contained important information such as names, addresses and some clinical information for nearly 3,600 patients.
A spokesman for CHLA said based on the internal investigation, the laptop has not been used to access the internet and the data could have been erased.
As a precaution, the hospital is sending out notifications by mail to all the families that could be affected.
Patients who are concerned may call (844) 299-6983 Monday through Friday between 6 a.m. until 6 p.m.