When the other children with the girl left her alone, the suspect allegedly approached her and forcibly took the money after asking her to make change for bus fare.
"The kids have the money in a clear bag, clear plastic bag. So you could see all the ones in the bag," the store owner told KTVU.
The children were selling candy to benefit their school.
"Ended up grabbing the child's arm, twisting it until she let go of the bag of money," said San Francisco Police Officer Gordon Shyy. "And took the bag of money and fled on the Muni 24 line."
The girl suffered minor injuries.
"It's not something that we see too often where an adult would prey upon a young person and rob them," Shyy said. "So it is alarming and we definitely want to bring this person into our custody."
The woman had previously come up short when trying to buy a $1.25 can of beer.
"She come in to buy a beer, but she didn't have enough money. She took that change and she left," the store owner told CBS San Francisco.