Police in Millburn say the family was unloading the two Range Rovers just before 2 a.m. Monday when they were approached by two armed men.
Police tell NJ.com one man held a 13-year-old child at gunpoint and the other pointed a gun at the other family members, demanding keys to the cars and cash.
One man drove off in one the family's vehicles; the other man couldn't get the SUV to start so he fled in a waiting car.
Police later found the stolen Range Rover in Newark.
The men wore hooded sweat shirts that partially concealed their faces.
No other information was available.