The pair were crossing Bridge Street at Summerdale Avenue when a 2002 Toyota Highlander turned left onto the road and hit them, PPD said.
Authorities were called to the scene just after 6 p.m.
Both victims were taken to Albert Einstein Medical Center where the woman, 26, is in stable condition. Her 4-year-old son was later taken to the Children's Hospital of Philadelphia where he is in critical condition, according to officials.
The driver remained at the scene and no arrests have been made as of Wednesday morning, police said. The investigation is ongoing.
Click here to follow Daily Voice Nazareth and receive free news updates.