A one-year-old child was found in the back seat of a car that was allegedly involved in a street race reaching speeds of 150km/h in Sydney's west, police say.

The 19-year-old P-plate drivers will appear in court next month after police allegedly detected their vehicles - a Ford Laser and a Suzuki Swift - racing along the Great Western Highway in Eastern Creek on Wednesday afternoon.

A NSW Police spokeswoman said officers from the Traffic and Highway Patrol Command were patrolling in Eastern Creek about 5.15pm when they allegedly clocked the drivers speeding at 150km/h in an 80km/h zone.

The officers pulled over the drivers - a male and a female.

"The passengers in the Ford, which was driven by the woman, included two adults and a one-year-old baby boy," police said.