Marcos Lopez-Garcia, 23, pleaded guilty to felony hit-and-run causing injury or death, and to misdemeanor charges of gross vehicular manslaughter without gross negligence and driving without a license, defense attorney Walter Rubenstein said.
Garcia faces five and a half years in prison when he is sentenced on June 29, Rubenstein said.
"He wanted to resolve the case because he feels bad for the family. He has cousins who are that age," Rubenstein said.
The 4-year-old, Christopher "Buddy" Rowe, was struck by Garcia's car in a marked crosswalk at the intersection of West Ninth Street and Rockwell Place near Jacob's Park in west Santa Rosa around 6 p.m. on Aug. 18, according to Santa Rosa police.
He was walking with his mother, Michelle Rowe, 45, his twin sister and a 6-year-old sister.
He died the next morning at Children's Hospital and Research Center in Oakland.
Santa Rosa police said Garcia was driving west on West Ninth Street and fled the scene of the collision afterward.
When officers broadcast a description of Garcia's car on the police radio frequency, Santa Rosa resident Leroy Flach heard it and drove to nearby Finley Park where he thought the driver might have fled after the collision.
Flach told police he saw the driver removing a decal from the rear of the car, and that the man was then picked up by a woman driving a silver Volvo, Sgt. Rich Celli said.
Flach provided the Volvo's license plate number to police, who found the car in the 500 block of Sonoma Avenue around 7:50 p.m.
Garcia gave police information that confirmed his involvement in the hit-and-run, and he was arrested and booked into Sonoma County Jail.
Rubenstein said the misdemeanor charge of vehicular manslaughter without gross negligence reflects Lopez-Garcia's contention that the crosswalk death was an accident.