@rajmca05 wrote:
I am newbie into DSLR and going through books, YouTube and practices. Was trying shallow DoF and looks like I am somewhat happy with it.
Lens used:Canon EF-s 18-135 USM, aperture priority mode. Auto focus in lens.
Objective: Shallow DoF. I kept wide open f3.5 of this lens and while zoom it’s changing automatically.
Just observed few things:
1. When kids are playing, images getting blurred. How we can ensure sharp and crisp images in this situation?
The main reason you will get blurry images is likely to be that your shutter speed is too slow. The way to establish this is to confirm that inanimate objects are clear (if they are close to your subject) and your kids are not. In that case you wouild switch to Tv mode and set the shutter speed at something around 1/120 sec or more - if ISO is set to automatic the camera will change ISO and aperture in order to keep the shutter speed you want. If all your items are blurry then it is likely to be camera shake or you are focusing on something else
2. Why I am not able to get a wide background on shallow DoF. I have to go very close to the object almost 135mm focal length but I loose the wide background.
Your camera has a range of what we call Fields of View (FoV). As the focal length of a lens increases the image gets bigger but the width of what it can see gets narrower (like using a telescope). If you want to get really close to something and have a wide background you will need a wide-angle lens, like a 10-22mm lens, but the lens you have is an excellent range for normal use, so I suggest you simple zoom out to the 18mm of your lens and move backwards and forwards until you get what you want in picture.
3. What are steps to change the focus point. I think it focuse to the nearest object but in some cases it focused to trees behind the object too.
You CAN change the cameras focusing system to reduce the number of focus points, but instead point your camera at what you want in focus, HALF press the shutter and then recompose the picture before fully pressing the shutter. You can make this easier to achieve by setting up what is call back-button focusing and you can see the details in your camera manual.
4. I am yet to use canon DPP, can we change the focus point and remove the blurryness too? If not then is it possible with photoshop? I am using RAW L setting.
Changing the focus point in post production is not a go. Even in RAW the focus point is set unless you use a high-end camera with dual-point focusing and even that is fairly marginal. It sounds like you need to practice focusing technique. I suggest shooting inanimate objects first then progressing to moving ones.
Regards
Raj
Hi Raj and welcome to the forum: 
I have given my responses in a different colour under each of your quesitons.
I suggest you look at your local library catalogue for a posting for Lynda.com- it it is available you free access to the excellent Lynda.com website that contains a huge range of videos on many subject, including a big catalogue of training videos from excellent instructors on all aspects of photography. If you don't have access through your library, go to the website and sign up for a free, no obligation month of access. I suggest you look for the Photography Foundations series by Ben Long, his videos will help you get started.
Doubtless you will get many more helpful posts. Just keep asking questions, but if you have not done so, get a copy of your camera's manual and read it. It will explain a lot and stop you getting testy comments from posters who will expect you to have done so! 
