(CNN) -- Their stay in Parvin State Park in southwestern New Jersey was supposed to be a getaway, a chance to enjoy the wilderness and quality time with family.
But when the line of strong storms came through shortly after midnight Saturday, two related families from nearby Millville decided to huddle together in a single tent hoping to ride out the strong winds and lightning together.
Then, after a particularly violent gust, a pine tree snapped -- and fell right on top of them.
By the time help made it to the scene, past downed trees and power lines, a 2-year-old boy was already dead, said Larry Ragonese, a spokesman for the New Jersey Department of Environmental Protection.
His 7-year-old cousin later died on the way to a hospital, the spokesman added.
"The rest of the family members miraculously were virtually unscathed -- a couple of scratches, but nothing to them," Ragonese told CNN. "What they have is the horror of what happened to the two boys."
The families weren't the only ones to experience tragedy when an extreme heat spell helped spawn a powerful line of thunderstorms that swept east from Indiana to New Jersey.
Millions were without power Saturday as a result, at a dangerous time given temperatures that soared past 100 degrees Fahrenheit in many of the hardest-hit locales. The combination of no electricity and extreme heat contributed to a host of unique challenges, leading officials to urge residents to do whatever they can to keep cool.
Scores of cooling stations were opened up and down the East Coast. At one, in Atlanta, workers unloaded bottles of water while a resident offered advice for the city's senior citizens.
"A lot of them don't realize that they are suffering from dehydration. And so to come to a place that is cool, come to a place where there's water provided, come to a place where they don't have to worry for about 7-8 hours in 106 degree temperature, it's really wonderful," said Savannah Potter.
Including the two boys from South Jersey, a total of 13 people died as a result of downed trees and power lines, officials said.
The millions lucky enough to survive the storms are hardly out of trouble, though, especially given the widespread power outages.
The strong winds, heavy rains and continued heat made it feel tropical, and certainly dangerous, in inland states like Ohio.
"It looked like a hurricane you would see on television -- the rain was falling horizontally, the patio furniture was moving," said CNN iReporter Louis Zur Muhlen from suburbs just north of Columbus, where he spotted burning power lines in the road.
"We have pretty severe weather with thunderstorms and such, but I have never seen winds like that, and I haven't seen this kind of damage."
Hospitals in Prince George's County in Maryland were buzzing Saturday as people came into emergency department waiting rooms trying to get cool, said Fran Phillips, deputy secretary for the state's Department of Health and Mental Hygiene.
Water was running out in Lowell, in southeastern West Virginia, because, without electricity, the town's water tanks couldn't be refilled, water and sewer operator Matt McLeish told CNN affiliate WTAP.
Residents in the town use about 50,000 gallons of water a day -- yet the main storage tank only has about 80,000 gallons left in it -- prompting officials there to urge people to conserve water.
In Rockville, Maryland, a mother and daughter were dealing with more ordinary, but still disappointing concerns. They were forced to cancel the young girl's birthday party Saturday at an ice skating rink after it lost power.
The family doesn't have electricity at its home.
"We're going to the mall. Montgomery Mall we hear has air conditioning so that's where we're off too now," said mom Alicia Lucero.
CNN's Nick Valencia, Jareen Imam, Athena Jones, Dana Ford, Maggie Schneider and Darrell Calhoun contributed to this report.