At least 10 children and teenagers were killed, with around 50 other children injured, some of them "hanging between life and death", a hospital official said.
French weekly Journal du Dimanche cited investigators as saying Bouhlel emptied his bank account, sold his vehicle and told friends about his radicalisation before the attack.
A French-Tunisian attacker killed 84 people as he drove a truck through crowds, gathered to watch a firework display during Bastille Day celebrations.
Health Minister Marisol Touraine said Sunday that one hospitalized person remains unidentified.
Former French President Nicolas Sarkozy, leader of the Republicans, said France's government was at war with violent jihadists and accused ministers of confronting them with "trembling hands".
Police ended his rampage by shooting him dead.
Who was the Nice attacker?
According to French media, a psychiatrist who saw him in 2004 said Bouhlel had come to him because of behavioural problems and that he diagnosed him as suffering from "the beginnings of psychosis". An Associated Press reporter at the site of the massacre, Nice's famous Promenade des Anglais, said the boulevard was slowly coming back to life.
Bernard Cazeneuve told France's RTL radio that while Mohamed Lahouaiej Bouhlel, a Tunisian living in Nice, may have been inspired by the terrorist network any "links for now have not been established by the investigation". Memorials for the dead have been set up on the westbound lane of the road where the victims were mowed down by Bouhlel. A man standing nearby said "Never here".
Investigations also showed he had grown a beard eight days before the attack, telling people "the meaning of this beard is religious". An argument ensued, with other passersby saying that his family deserved respect.
Many family members have been frustrated by a lack of information about their missing loved ones.
Many blame Mr. Hollande's Socialist administration for not doing enough to prevent terrorism in the country that's seen three major Islamic State-inspired attacks in the past 18 months.
"All debate is legitimate, but this attitude of putting the unity of the country into question just plays into the hands of the terrorists", Valls said in the interview.