They say the boy crossed the street mid block and was struck by a blue Honda traveling eastbound.
The child was rushed to the hospital and is in fair condition, officials say.
SFPD says the driver remained on the scene and is cooperating with investigators.
Impairment is not being considered as a factor.
#SFPD is investigating an auto vs. pedestrian collision on the 1800 block of 25th St. At approx.4:06pm a 3 year old boy crossed the street mid block and was struck by a blue Honda traveling east bound. He was transported w / non life threatening injuries. pic.twitter.com/6KqpHfOWHC— SFPDSgtMike (@SFPDSgtMike) March 30, 2018