All four were wounded, and the youngest of the victims was given emergency surgery because of her wounds.
A man, 37, was arrested trying to leave the scene in a vehicle after the attack, which happened around 09:30 local time (07:30 GMT) near Sisteron.
Local prosecutor Raphael Balland said the motive was still "very vague".
The mother, 46, and her daughters aged eight, 12 and 14 were regular visitors to the holiday camp at Garde-Colombe and had been having breakfast when they came under attack. All four were taken to hospital and the youngest suffered a punctured lung, reports said.
According to authorities, the suspect in custody was of Moroccan origin and had been staying on the site with his own family next door to the victims.
Although he had been in trouble with police many years ago, reports said there was no indication of a religious link to the case.
Unconfirmed reports suggested he had objected to the light clothing worn by his victims but Mr Balland said "it's all rumour, the man's not said anything".
A woman and her three daughters have been attacked by a knife-wielding man at a holiday camp in the south of France, French media report.