The crash occurred in the area of Keele Street and McNaughton Road just before 6:30 p.m. on Tuesday evening.
York Regional Police say that an Acura MDX was heading south on Keele Street when it crossed the centre line for unknown reasons. That vehicle collided with a Subaru Forester and a Pontiac Enclave that were in the northbound lanes.
An eight-year-old boy was taken to Sunnybrook hospital. On Wednesday, police said he suffered non-life threatening injuries as a result of the crash. His injuries were initially reported as being more serious.
Police want to hear from any witnesses they haven't spoken to yet.
Anyone with information is asked to contact investigators at 1-866-876-5423, ext. 7704.
Information can also be passed on anonymously through Crime Stoppers at 1-800-222-8477.