I came to US (H1B visa) for first time in February 2013 and my wife and kid will be joining me in US (H4 visa) during December 25 2013..

1) Can I file as "married filing jointly" and apply for ITIN for my wife and kid when I
File Tax for 2013?
2) Can I include my child as dependent when we file taxes for 2013?
3) What deductions can be claimed as I am the only earning member and supporting wife and kid?

You will be allowed to file jointly irrespective of when your wife comes to the United States. However, you must claim her income on the tax return, then claim the Foreign Tax Credit (Form 1116) or exclude the income using Form 2555.

You will NOT be able to claim the child, however. To claim the child, he must spend at least 31 consecutive days in the U.S. In 2013, which means he must be here by 1 December 2013.

If you need professional help filing for 2013, email me at the email address in my profile.