The stabbing was reported at 5:36 p.m. in the 1000 block of Scott Street.
Police found an 8-year-old boy and a man with stab wounds.
The boy was rushed to a trauma center in critical condition. The man was released from the hospital.
Police arrested 38-year-old Fairfield resident Lythia Bouie. She's in jail on two counts of assault with a deadly weapon, child endangerment and domestic violence.
Police say they found both victims on Scott Street near Matthew Drive after getting 911 calls about a disturbance.
The investigation is ongoing and police would like to hear from anyone who might have witnessed what led up to the attack.
Bay City News contributed to this story.