Wildwood police and firefighters responded to the Beachside Resort on the 3700 block of Atlantic Avenue just before 6:30 p.m. Friday for a possible drowning.
They arrived to find witnesses performing CPR on the child and took over the resuscitation efforts.
The boy was taken to Cape Regional Medical Center where he was pronounced dead a short time later.
"Unfortunately, the efforts of our first responders and the hospital medical staff were unsuccessful in reviving this young child," a joint press release from the police and fire departments said Saturday.
The incident remains under investigation.
"We are absolutely devastated at this tragic and senseless loss of a life so young. We strongly encourage everyone whenever you're swimming, swim near a lifeguard, especially when on our beaches. At commercial or residential properties which are not required to be guarded, please be extra cautious," the release said.
Authorities said adults should monitor their children while swimming and use a life-vest or other approved personal flotation device.