They are the youngest victims in a heat wave which has claimed more than 50 lives across parts of south west America.

July could be hottest month in US for 600 years

The four young cousins clambered into the car boot to hide during a game.

Their parents drove the car around the neighbourhood to search for them without realising they were inside. After 45 minutes, an aunt heard a gasp and opened the boot.

The youngest - Brianna Rohan, 2, Ramon Torres, 3, and Steven Dawson, 5 - were dead. Six-year-old Christina Rohan died later in hospital.

The heat is also thought to be responsible for at least 23 deaths in Texas, six in Oklahoma and at least 20 in Louisiana since mid-May.

Gore blames fossil fuels

Vice-President Al Gore is blaming the heat wave on greenhouse gas emissions and is appealing to Americans to cut down on the use of all types of fossil fuel.

The elderly are especially vulnerable

Officials warned those outside to take breaks, and those who had elderly friends or relatives to check on them.

Air-conditioned public buildings in Texas are being kept open as cooling centres, but weather forecasters are saying there is no relief in sight.

Temperatures in Texas have been above 100º Fahrenheit (37º Celsius) for nearly two weeks, and are expected to keep on rising.

Scientists say that July could end up as the hottest month in the United States for 600 years.

Spoiled crops

Crops have withered

The blistering heat is also being blamed for ruining crops across thousands of acres.

Farmers and ranchers in Texas are expected to lose around $1.5bn, while damages in Georgia are estimated at $400m.