A small whirlwind known as a dust devil tore the inflatable from the ground at a fairground in Yucheng county.
One parent reportedly told local media that she saw children fall from a height of about 20 metres (66ft).
A county government official told the South China Morning Post it was unclear whether "human factors" played a role.
Local authorities said 18 other children and two adults were taken to hospital. One child was in a serious condition while the rest were being treated for minor injuries.