Luca Green, of Finch Close, Uppingham, died on Monday morning at John Radcliffe Hospital, Oxford with his parents Sharon and Stuart by his bedside.
Their only child had enjoyed his party with some friends on Saturday afternoon, the day before his birthday. But after going to bed complained of a headache at about midnight.
The Uppingham Primary School pupil was rushed to Kettering General Hospital and transferred to John Radcliffe Hospital where he was put on a life support machine.
His friends and fellow pupils were told of his death on Tuesday during a special morning service at the school.
Headteacher Janet Anning also sent out a letter to parents informing them with sadness and shock the sudden death of a model pupil.
Luca was a popular boy who was a member of Uppingham Beavers, the school arts club and maypole dancing team. He had been looking forward to performing at Lyddington Fete tomorrow.
Children in Luca's Year 3 class, led by teacher Isobel Newbold, have been putting together a booklet of pictures and memories of their friend. It will be presented to Luca's parents.

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One pupil wrote: "I wonder if Luca can still smell flowers in heaven?"
Another said: "Luca always made us laugh."
Mrs Anning said: "Luca was a lovely, gentle, caring boy – a model pupil. He contributed to outside activities, enjoying art club and was set ready to perform as part of the maypole dancing club at Lyddington on Saturday.
"He was extremley well mannered, polite, diligent, he always got on with his work and he always did his best.
"He was caring, friendly and well liked – a genuinely lovely boy. He will be missed and always remembered in our heads and our hearts. We all offer our sincere condolences to his parents."
Father Peter Edwards of St Peter and St Paul's Church helped lead the Tuesday assembly and spent time with Luca's class during the morning.
He said: "He was a very nice, lovely, well behaved boy. Hard working and friendly, he will be greatly missed by all who knew him.
"He had wonderful qualities he brought to life and to the family and the school.
"It is a shock when a member of the school community, especially one of the children, dies in such appalling circumstances."