Dajahnel Young had been on a trip to the seaside town of Margate with people from her church when she disappeared.
Some 6,500 people flocked to the busy Kent beach on July 28 2018, during a spell of hot weather.
An inquest heard that Dajahnel, from Erith, south-east London, was one of 25 children reporting missing on the beach that day.
She was discovered floating lifeless in the sea at around 3.13pm and was pronounced dead in hospital after resuscitation attempts failed.
An inquest into her death has been taking place at the Guildhall in Sandwich and concluded on Monday.
Coroner Alan Blunsdon concluded that Dajahnel's death was an accident and made no finding of neglect against husband and wife Cynthia and Fitzeroy Robinson, who had been leading the trip.
He said: "A moment of inattention is a nightmare faced by many parents on a daily basis, including on Margate beach where it was the nightmare experienced by 25 parents."
Mr Blunsdon said he did not believe this death represented a gross failure.
Referring to Dajahnel by her nickname, he said: "I have identified evidence to find that Amazin entered the water intentionally but did not realise that action would lead her into peril."
However Mr Blunsdon added that Mr and Mrs Robinson did not give Dajahnel their permission to go into the sea.
"Amazin did not enter the water with their knowledge or consent," he said.
The coroner also said he was "not persuaded" that Dajahnel's mother had actually instructed Mrs Robinson that she was not to go into the water.
"I think her recollection has failed her to a little extent," he said of Miss Remekie.
Following the conclusion, Mrs Robinson's lawyer, Nick Fairweather, said that the inquest had led to a "distressing, chilling and menacing case of trolling".
Earlier in the inquest, Dajahnel's mother Camille Remekie said that she entrusted friend Mrs Robinson to look after her daughter, who could not swim.
Miss Remekie said she was initially reluctant to allow Dajahnel on the trip because she did not want her going into the "dirty" sea water, but gave permission "at the last minute".
The mother, who was working in Bexleyheath on the day her child drowned, said Mrs Robinson was one of the only people she trusted and felt her daughter "needed a break" after being at school.
But Miss Remekie, who claimed she still does not know exactly what happened to her daughter, said she told Mrs Robinson "about two times" before the trip: "I do not want her going into the water."
Mr Fairweather, representing Mrs Robinson, told the hearing his client denied that Miss Remekie told her not to allow Dajahnel into the sea.
Mrs Robinson was quizzed about the account she gave about what the six-year-old had been doing before she went missing.
Mrs Robinson said that Dajahnel was with her husband, Roy, at the seashore, "splashing around" with other children, before needing to go to the toilet.
Mrs Robinson, who was looking after four other children at the time, said: "She said she wanted to wee, but by the time (she walked back to me) it looked like she waited until she was bursting - so she (wet) herself."
Representing Dajahnel's family, Laura Profumo said a child had recalled Mrs Robinson telling the six-year-old to go "down to the sea to wash her hands". Mrs Robinson said she did not say this.
Speaking outside the inquest, a tearful Miss Remekie said she feels her life has been "destroyed" by the death of her daughter.
She said: "Amazin was happy, she was bubbly, very, very friendly and she loved life."