Police say two people became concerned after seeing the youngster in a vehicle outside the McDonalds in the 2400 block of S. West Street at around 5:40 Sunday evening.
Police say the heat index at that time was around 95 degrees.
When officers arrived, they found four children (ranging in age from three to six years old) and their 31-year-old father. Police say the three-year-old was left in the car while the father and the other three children went inside the restaurant.
The father was arrested on child endangerment charges.
The children, who were not hurt, were released to other family members.
Police spokesman Lt. Doug Nolte says he isn't sure if the car was left on or if the child was in a car seat.
"Leaving a child in a vehicle, regardless of weather conditions," Nolte said, "is not acceptable."
Lt. Nolte added that it is good that someone noticed what was going on and called police.