I think you have done a lovely job. You've obviously taken the time to figure out some of the keys to great portrait shots. For example you've used window light from the side like a big soft box and you have chosen a good lens (50mm) etc. f4 is a good place to start because you still get some background blur yet your depth of field is still a bit more forgiving when shooting children. Good work.


There are also some simple fixes you can work on. Sharpness is a big one, maybe not so simple but important. Speeding up your shutter speed will help. You're already on high iso so stopping up a tad might help. More light will get you there also. If a tripod is a possibility then take advantage of that also. Good luck taking shots of kids with a tripod though.


Strobes are great, but don't give up on natural light. There are plenty of tricks to get the most out of it. Moving outside will increase you available light, pick a shady spot that has a large area of bright light adjacent. This bight area will bounce light onto your subject and give a flattering light as well as some nice catch light in the eyes (place you subject in the shade not the bright light), I think your shots reveal that you are already on the right track here. Search 'you tube' for natural light photography and you'll find some great tips that will propel you further in this direction.


Finally try some simple tweaking in post production. Post production is the other half to your photography and is a skill that needs to be honed like any other. Have a look at some basic edits I made to your first two images (hope you don't mind):


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Here I just increased the contrast, you can do this with levels or curves, I used the black slider in Light Room. Next I cropped the image, as a rule you should crop above the joints not below. Check out this tutorial for more info on cropping people shots: http://www.youtube.com/watch?v=c8AC4VeIgkg


Finally I sharpened the image and added a vignette.


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I've done similar edits here but also increased the exposure and warmed the image by using the temperature slider in LR. I think I over did it with the sharpening but you get the idea. []


These edits literally took less that 2 min per image - truly.


You've done a great job with your portraits - keep it up, you family will thank you for it in the future.