The attack was reported at about 4:30 p.m. at the Koret Children's Quarter near Kezar Drive in the southeast corner of the park, police spokesman Officer Gordon Shyy said.
The suspect, Sabryna Bell, allegedly walked past a father and his daughter and, for no apparent reason, kicked the nearly 2-year-old girl in the chest, Shyy said.
The girl fell and hit her head on the pavement, but her injuries are not considered life-threatening. She was in San Francisco with her family from out of state to be a flower girl at a wedding, Shyy said.
Bell also allegedly walked up to another parent and threatened to kill other children, then fled, Shyy said.
She was apprehended a short distance away, and was booked into jail on suspicion of assault with a deadly weapon, making criminal threats and inflicting injury upon a child. She had outstanding warrants for her arrest, Shyy said.