According to authorities, a deputy vehicle and a Toyota truck collided near the intersection of TC Jester Boulevard and Tomlinson Trail at about 12:40 a.m.
The sheriff's office said the child, under 12 years old, was in the front passenger seat of the Toyota without a seatbelt when they were ejected during the crash.
The deputy involved in the crash gave the child CPR at the scene before the child was taken to a hospital and pronounced dead, investigators said.
Authorities said the crash was not serious enough to cause a death, and that the child would have survived had they been wearing a seatbelt.
Deputies said the Toyota driver, described as a man in his 50s or 60s, showed signs of intoxication.
Investigators said they plan to request a search warrant for blood, and if the driver is found to be intoxicated, he will be charged with intoxicated manslaughter for causing the child's death.
The sheriff's office said the deputy had a clinician in the passenger seat, who was injured too. Both the deputy and clinician were taken to the hospital for minor injuries, HCSO said.