BOSTON -- Local emergency room doctors are sounding an alarm after four children who nearly drowned were rushed to Children's Hospital last weekend.

Dr. Mark Waltzman, a doctor in Children's Hospital emergency room, said the number of close calls in recent weeks has rattled him and his colleagues.

“All of this white is pneumonia,” said Waltzman, pointing to a child’s X-ray. “Fluid in the lungs from the child breathing in the water from the swimming pool.”

"Even if they're perfectly fine by the time they arrive here, they are at risk of developing lung problems within the first 12 to 24 hours," he said.

Already this summer there have been numerous examples locally of the danger open water can pose. On June 21, a 2-year-old Stoneham boy nearly drowned in a home swimming pool. In May, a 22-year-old Lynn woman who had graduated from college just days earlier was swept out to sea near Plum Island. Her body was found a few days later.

Waltzman said young children are most at risk of drowning. Toddlers, especially, he said, are curious, and most are unable to hold their heads above water.

"Toddlers just take off," Waltzman said. "People aren't watching their children as diligently as they should be, and next thing they know, they look in the pool and there's a child 1- to 4-years-old just floating in the pool."

According to the most recent data available from the Centers for Disease Control and Prevention, more than 3,400 Americans died by unintentional drowning in 2007 -- nearly 10 lives lost every day. One in every five drownings is a child younger than 14.

Waltzman said adults must follow one simple rule.

"Parents really need to keep an eye on their kids constantly if there's a pool there," he said. "At all times, they need to be within arms reach."

Waltzman said water isn’t the only risk for children during the holiday weekend. They see a children who have been burned and worse by fireworks.

"We still lots of those kinds of injuries, and kids shouldn't be playing with fireworks," Waltzman said.

Waltzman said summer, in general, is trauma season in the E.R. and lots of children get cuts and broken bones. He said they should always wear helmets, pads and seat belts.