For millions of kids, August is defined as the month after camp and before school. The month, in other words, when every day is spent tearing up the backyard.

If littered with the wrong toys, and wrongly supervised, that can be the worst place for them to be. Look at the numbers: The Centers for Disease Control and Prevention estimates that 200,000 children ages 14 and under are treated in emergency rooms for playground-related wounds each year. Just 26 percent of the types of injuries occur on home equipment, according to the Consumer Product Safety Commission; most of the damage comes on public playgrounds. But when looking at death, a full 90 percent from playground equipment, according the same group, occurs at home. Home jungle gyms and swing sets are less likely to be anchored properly or installed on a protective surface. And most parents get lulled into a false confidence knowing their children are "safe" when they're nearby—less than 25 percent of parents closely monitor their kids on play equipment at home, according to a survey conducted by the Home Safety Council in 2008.

View Our Gallery of the Worst Backyard Hazards

So which backyard fun-factories pose the greatest risk for injury? To figure that out, we combed the CPSC's National Electronic Injury Surveillance System online database, which contains hospital injury reports from 96 hospitals across the U.S. The CPSC categorizes the data by the product associated with each injury, and using weighted, historical data, then extrapolates an estimated figure for total injuries.

We limited our list to include only reported injuries for children ages 10 and under in 2009 and only for specific products that are typically used for backyard fun. For certain categories including bounce houses, we extrapolated the data using the injury report description of amusement rides.

The results aren't perfect; hospital incident reports can be inconsistent and opaque and the CPSC's estimates take several factors into consideration. And these results don't take into account the relative popularity of certain activities—yes, the monkey bars send a lot of kids to the hospital, but untold millions spend their days getting more dexterous, swinging bar-to-bar. But they are also a sobering reminder that what gives joy can also give pain, and that children merit a careful eye, even in the confines of home.