Tributes have been paid to Summer Grant, of Braeford Close in Norwich, who died when the inflatable was apparently swept some 150m across a park in Harlow, Essex, on Easter Saturday.
Police said the autopsy established the cause of death as multiple injuries.
A man, 27, and a woman, 24, both of Cambridgeshire, were arrested on suspicion of manslaughter by gross negligence following the child’s death, and were released on bail pending further inquiries.
Almost £2,000 (€2,530) has been donated in an online fundraising drive for Summer’s family. The fair at Harlow Town Park was closed yesterday but a steady trickle of people visited the park, leaving messages to a “princess” and an “angel”.
A sudden gust of wind blew the bouncy castle off the ground, Ray Smith, from the Showmen’s Guild of Great Britain said.
“It was a sudden gust. Had it been a consistent wind they would have closed down all the inflatables.”
He said the firm running the bouncy castle was the family-run Thurston fun fairs. Asked about how bouncy castles are set up, he said: “I know the family and I am very confident they had staked it out properly.
Police said that weather conditions on the day will be a factor in a “lengthy” and “complex” investigation.