Police were in the area for a separate incident when they alerted the fire at 2:19 am, officials said.
Passers-by tried to enter the house to rescue the family, but were prevented by the heat and smoke. When firefighters arrived, flames rose from the roof, emergency officials said.
Firefighters managed to enter the house through a window and quickly found two children who were handed over to paramedics. The children died on the spot.
Firefighters continued their search and found another child and a deceased adult woman, the firefighters said.
Investigators are now working to determine the cause of the fire. The firefighters said most of the damage was located at the back of the mobile home and has spread to the front.