The Daily Herald reports the couple allegedly smoked meth while the girl was with them in their vehicle.
The girl's 22-year-old mother, and her half-brother boyfriend were charged Thursday with one count each of child endangerment with a controlled substance.
The woman has other children and Child Protective Services is involved.
Marysville Police say they were tipped off by a 911 caller who was worried that the girl was being exposed to second-hand smoke from the drug. It was 38 degrees that night and the vehicle had no heat. Police say the girl was dressed only in a diaper and appeared to be cold and hungry.