I don't know about the rest of your images, but in this one you have a classic case of a very dark, prominent color fooling the camera's meter into overexposure. Camera meters measure light reflected off of your subject. A black object reflects 9% of the light hitting it, and a white object reflects 36% of the light it receives. Since your camera meter can't tell what color your subject is, the manufacturer sets the meter to correctly measure the light reflecting off of a medium-toned image, something that reflects about 18% of the light that hits it. That's why folks talk about using an "18% gray" card. If your subject is very dark, the meter will think that there is less light hitting the subject, and will overexpose. A very light object will be underexposed.
So, what happened in this shot is that the meter saw that black coat and thought "Oh, my. There's not enough light here." It overexposed the image and the boy's face was blown out. You can easily solve this by working in manual mode. You need to realize when your subject is not a medium tone, then adjust your exposure to compensate. You can also do this by using the exposure compensation function, but I find it's just easier to work in manual mode. Just follow this simple rule: If it's dark, make it darker. If it's light, make it lighter. In other words, underexpose a dark image to keep it dark, and overexpose a light image to keep it light.
The new cameras coming out now have a separate sensor to assist the meter in judging what color an object is (I may be wrong, but I believe the 7d is Canon's first with this feature), so this type of exposure error may be a thing of the past soon. Nikon has had this feature for a few years now, so it surprised me that Canon is just now catching up.
Until you can upgrade to a new camera body, you can print off a gray card from any one of many sources on the internet. Use it as a guide to see if your subject is the same tone. You can place it in front of the camera and take a meter reading off of it, then set your camera in manual mode and use those settings for your picture. Once you get an eye for reading the tone of a subject, though, you won't need the card.