A four-year-old Philadelphia boy was in critical condition and undergoing emergency surgery Saturday night after he found a gun beneath his mother's pillow and shot himself in the chest, police said.

The shooting happened around 6:55 p.m. inside a bedroom of a house on the 6200 block of Cardiff Street in the Mayfair section in Northeast Philadelphia, police said. Authorities said the youngster shot himself once in the left side of the chest with a .38 caliber handgun.

It was not immediately clear who else, if anyone, was home at the time of the shooting. A police spokeswoman said late Saturday that detectives would interview the boy's mother at some point.

"All we can tell is, it was accidental," 15th District police officer Chris Bennett said Saturday night.

The wounded boy was in surgery at St. Christopher's Hospital for Children, police said.

A neighbor who spoke on condition of anonymity said the house in question appeared to be occupied by a woman and several children who had lived there for no more than a few years and who mostly kept to themselves.

"I see the little four-year-old boy all the time," often walking with his mother, the neighbor said.

In the summer, the family would place a swimming pool on their postage-stamp front lawn so that the boy and others could play. In winter, the yard became home to a miniature basketball hoop - perfect for a four-year-old.

The rowhouse block is a draw for first-time homebuyers. Asked if it was the kind of place where residents felt the need to keep firearms by their bedsides, the neighbor said it was nothing of the sort - neither a target of vandals or nor of violent criminals.

In fact, the neighbor said, the nearest police station is two blocks away and visible from residents' front stoops. "Our neighborhood's quiet," the neighbor said. "Everybody looks out for everybody."