The sedan did not stop and turned left onto Chapel Rd.
Kaur said the car came within two inches of her pregnant belly but she was too worried about her crying son to think about it at the time.
Karamveer didn't want to put weight on his injured leg and they noticed some swelling and a cut, it wasn't until they got an x-ray that they knew it was broken.
Two police cars and an ambulance attended the incident.
Counties Manukau Senior Sergeant Jono Chappell said this is a serious matter which left the mother and children shaken.
"Failing to stop and render assistance following a vehicle crash is a criminal offence.
"The fact that this person did not stop to see if the child was okay is appalling and we would like to identify the owner of the vehicle so we can make further inquiries."