Three live rounds were in the gun and another round was found on the floor in the school, police said.
Karen Divittorio's children have played with the alleged 8-year-old seller, who lives right next to her home.
Now, he's charged, as a juvenile, with 3 counts of criminal possession of a weapon.
"You can't blame the kid. You can only blame the parent," said Karen Divittorio.
The boy's father, 54-year-old Ignacio Galvin, is charged with 3 counts of criminal possession of a weapon and with acting in a manner to injure a child.
At P.S 107 where the alleged sale happened, parents worry about the potential for utter disaster.
"Loaded, too, no less. That's what scares me more," said parent, Sharon Filomena.
"It's really a sad situation when you have an 8-year-old who brought a gun into school and then sold it for 3 dollars. That's something that can't be tolerated," said School Chancellor Dennis Walcott.
The boy's father told investigators that he bought the gun for his own protection, according to Police Commissioner Ray Kelly who added that there are simply too many guns out there and that this is an indication of that.
"We, in the last 2 years just in buy-back programs in churches, have bought back 6500 guns. That's an indication of what's happening. Here you have a young boy who sees a gun in his house and sells it so there's no question about it. It's an issue," said Kelly.
The commissioner says the boy grabbed the gun right off the top of the refrigerator. A spokesman for the schools says disciplinary action is pending against both the seller and the buyer.