The victims, sisters ages 3 and 14, died in the hospital, while another sibling was slightly injured and their parents were unharmed, Italian news reports said.
Most of the other campers near Marina di Massa, a town on Tuscany’s coast, had fled the campground after storm warnings on Saturday.
Winds up to 93 mph whipped Italy during the night, also fueling an arson fire in woods near Palermo, Sicily.
The blaze forced 1,700 people from their homes in the town of Altofonte on Saturday night.
Sicily Gov. Nello Musumeci said the fire, which was still burning Sunday, was deliberately set in six locations.