A brother and sister who got into difficulty in the sea died in a "tragic accident", a coroner has ruled.
Malika Shamas, 14, was pulled from the sea at Clacton, Essex, on 8 August and died later in hospital.
She had been in the water with her brother Haider Shamas, 18, who died two days later, and a cousin who survived.
Their mother Shagufta Shamas said she wanted to ensure safety precautions were in place "so an incident like this does not occur in the future".
The inquest in Chelmsford heard the Shamas siblings, who could both swim, and their cousin got into difficulty near Clacton Pier at about 13:40 BST.
Det Insp Craig Wiggins said Malika, from Luton, was at a point where she was still able to stand up.
He said she "panicked" and her brother and the other children tried to help.
Malika died of immersion while her brother died two days later of pneumonia, brain damage and drowning, the inquest heard.
Mrs Shamas said she struggled to stay upright when she tried to help/
"The sand underneath my feet was giving way... this happened within minutes," she told the inquest.
"Should there not have been signs in this particular area saying you should not go in and that this is what can occur?"
The inquest heard the area where it happened was just out of range of the nearest beach patrol.
Essex senior coroner Caroline Beasley-Murray said she was minded to write a prevention of future death report dealing with the warning signs near the scene.
The inquest heard there was a warning sign on a nearby flood defence which said "danger, no bathing due to varying depths of water" but the coroner noted that you had to be quite close to read it.
She said some warning signs could be in a larger print and, after a suggestion from Mrs Shamas, said they should appear in a child-friendly format.
Tendring District Council said its signs met national standards.
The siblings died little more than a year after Ben Quartermaine, 15, drowned while swimming with a friend off Clacton Pier.
The coroner told Mrs Shamas she had "displayed the utmost dignity" throughout the inquest.
"They were clearly very much-loved people with bright futures ahead of them. I do hope you will be able to look back on the happy memories you have of them both," she said.
Mike Carran, head of sport and leisure and Tendring District Council, said after the hearing: "Nothing can bring back these teenagers who had their whole lives ahead of them.
"However, we hope that this tragedy will help to raise awareness of the dangers inherent at the coast, particularly with the more difficult-to-reach inland communities, and to also help to prevent further tragedies."
Mr Carran said the council would review its signs in line with national guidance and send safety leaflets to coach companies and print messages on the back of train tickets in the aim of reaching holidaymakers.