(NEWSER) – Drivers on the Bronx River Parkway were a little surprised to see a 6-year-old driving his miniature ATV beside them last night. The boy's mom was even more surprised to discover him missing. It started on a family trip to a park in Mount Vernon, New York, where the autistic boy rode off unnoticed at around 7pm, the Journal Newsreports. "They realized pretty quickly he was gone but couldn't lay eyes on him," a police spokesman said. Bystanders say the mother was frantically calling for her boy as kids ran back and forth looking for him, 7Online reports.