Jake Walter Nicklaus was pronounced dead at Palm Beach Gardens Medical Center, Palm Beach County sheriff's spokesman Paul Miller said.
The son of Steve and Krista Nicklaus had been playing in the hot tub with his 4-year-old brother and their nanny at the family's home, Miller said. The three left the pool area and went into the house, but Jake slipped away and went back through a sliding door to the hot tub, Miller said.
The nanny quickly realized he was missing and discovered him in the water, Miller said. She performed CPR until emergency workers arrived. The boy was breathing at the time, he said.
He was brought to the hospital and died shortly after rescuers were called, Miller said.
According to the preliminary investigation, the death appeared accidental and there was no reason to suspect foul play, Miller said. An autopsy was planned to confirm the cause of death.
He said there was a child barrier around the entire pool area.