The girl fell ill as parents were collecting children from Willow Bank school in Woodley, Berkshire, last Thursday.
Despite teachers frantic efforts to save her, she tragically died.
A shrine of teddies, cards and flowers have been left outside the school in tribute to the girl, who has not been officially named.
Among the cards is one which reads: "My beautiful, happy little girl, Lilly-May. Mummy loves and misses you so much. Why did you leave us? You dance with the angels now.
"Love you more Mummy."
A Thames Valley Police spokeswoman said the death is being treated as 'unexplained but not believed to be suspicious'.
A statement posted on the school's website last Thursday said: "We are deeply saddened to report that one of our children passed away today.
"Our thoughts are very much with the family and friends at this tragic time."