Some of the misfocused shots could be caused by changing the focus plane when recomposing, this article does a good job of explaining how this can happen:
http://duncandavidson.com/2008/09/focus-and-recompose-exposed.html.
It's definitely possible to get nice outdoor portraits without a flash, you'll just need to be mindful of your conditions.
When shooting portraits outdoors without flash I usually shoot with the following, basically the same as what Mr. Sandman suggested:
- AV mode in order to control the depth of field and use exposure compensation if the background is significantly darker or brighter than the subject.
- ISO as low as possible depending on conditions, usually 100 or 200 but will go higher in order to keep shutter speeds up to prevent motion blur when handholding.
- I always shoot in RAW
- Focus point will depend on how I'm framing the shot but for close ups I always focus on the eyes.
- Diffused light from clouds or shade can help a lot.
I use flash both on and off camera quite a bit outdoors but here are a couple snapshots that were ambient light only, please disregard the wild hair and food/dirt on my daughter's face, both were taken when she was playing in the yard and weren't meant to be formal portaits.
I used these two as examples because both of them were shot with a very thin depth of field using an 85mm lens at f/2.5 and f/2.0, respectively. If we estimate that the camera was six feet away from her when the shots were taken then the area in focus was approximately 1" from front to back. If I had swung the camera to left or right after locking focus the chances are very good that her eyes wouldn't have been in sharp focus and the images wouldn't have been worth keeping which gets back to my original comment about the focus plane changing when recomposing.
Back to the images you posted, here is an edit of the older boy. I increased saturation and contrast using adjustment layers, then flattened the image and ran an unsharp mask on it. I also cropped the image because it looked awkward to me with the boy being cut off at the legs and still having so much visible background above his head.
It looks like you had good diffused light for these shots, I would imagine they were taken on a cloudy day. If the light is harsher you can use a piece of white foamcore or even a piece of cardboard with some aluminum foil stapled to it as a reflector to provide some fill light. It's a low cost way of improving your shots when you don't have a flash readily available.
Hope this helps. Keep shooting and posting! If you decide to get a flash then there are a lot of other possibilities that you can explore.
