The incident took place Friday night at 8 pm near a toll plaza on the national highway in Rewari, they said.
The occupants of the car were going to attend a marriage function in Gokulgarh village in the district.
Rajinder, 60, the father of groom Jatinder, was among those killed, police said.
The other deceased have been identified as Daksh, 7, Prachi, 7, and Kaku, 5, and driver of the car Papinder.