The baby had been admitted in serious condition to a Paris children's hospital after the accident and died there hours later. The other victims - adults and several children, all of African origin - were hospitalized with multiple traumas, the judicial official said.
Circumstances surrounding the early-morning incident were unclear and it wasn't known if the victims jumped on purpose or were forced to, the official said. There was no emergency, such as a fire, in the building at the time.
An initial investigation suggested they jumped after one of the women involved became hysterical and started shouting she'd seen the devil, the official said. However, French television reports suggested the tragedy occurred when one of the men living in the apartment entered a room where the others were watching TV after taking off all his clothes.
Two men - a 30-year-old and a man who jumped out of the window holding a 2-year-old - have been taken into police custody, the judicial official said on condition of anonymity in keeping with her job's regulations.
The apartment building is located in the Paris suburb of La Verriere.