A two-year-old girl died in hospital after falling in the sea, police said.
The toddler was airlifted to a London hospital in a critical condition after being recovered from the water at the Warren Apron near Folkestone, Kent, just before 3pm yesterday.
However despite efforts to save her, she died yesterday evening, a spokeswoman for Kent Police said.
An eight-month-old boy who also fell in the sea was taken to the William Harvey Hospital in Ashford where he was said to be in a stable condition.
Dover Coastguard said it was contacted after reports that a child's push chair had tumbled into the water.
A spokesman said the Dover RNLI lifeboat was launched but the two children were rescued by members of the public, who pulled the toddler out of the sea unconscious.
Two adults, a man and a woman, were also taken to hospital in Ashford as a precaution.
A spokeswoman for South East Coast Ambulance Service said: "They were cold and wet and obviously shaken up.
"The two children were in a more serious condition."
A spokeswoman for the RNLI said that an off-duty member of Dover lifeboat crew administered first aid to the children.
Lifeboat volunteer John Miell was walking his dog between Dover and Folkestone when he heard cries for help.
"He ran to the scene and on the water's edge were two adults and two children who had been in the water," the spokeswoman said.
"He administered CPR until the emergency services arrived."
She said that other passers-by appeared to have helped them out of the water.
The RNLI lifeboat sent a recovery vessel to the shore and coastguards from Folkestone also attended.