Dylan Cecil was on holiday when he fell into the water at Burnham-on-Sea in Somerset last Sunday.
He was said to have been trying to get a closer look at the sea when the incident happened.
Coroner Michael Rose said a post-mortem examination showed Dylan drowned.
No members of Dylan's family were present at the short hearing when his inquest was opened in Taunton.
It was adjourned until a date yet to be set.
The relatives of Dylan Cecil, who slipped into the sea from a jetty, say they are grateful after police believe they have found his body.
The mother of Dylan Cecil says is "devastated" but will stay in Burnham-on-Sea for "as long as it takes" until her son is found.
The search for a four-year-old boy - who went missing in the sea while on holiday - has been called off by rescuers.