I'm here in US on a L-1B visa. I came here with the family (Wife and Son) on Sept 23rd. Can I eligible to apply as a resident alien? I'm planning to apply for the ITIN for my son.

You have two choices for 2009
Choice 1: File non-resident tax return. You can deduct moving expenses if not reimbursed by your employer.
Choice 2: You can file resident tax return as Married Filing Jointly. You will have to wait for 5 months to file your tax return till you meet the Substantial Presence Test in 2010. Your U.S. Tax Return: Substantial Presence Test

You will get standard deduction of $11,400 and exemptions ($3,650 each) for both of you and the kid. You will also get child tax credit of $1,000 each.

You must both declare your worldwide income for 2009. If you have any foreign income, and on that income you paid taxes in the foreign country, then you can claim foreign tax credit (Form 1116) or you can use Foreign Earned Income Exclusion (Form 2555). Read: Your U.S. Tax Return: U.S. Citizen or Resident with Foreign Income

You will complete forms W7 (application for ITIN) for your spouse and children and attach with your tax return. You can also deduct moving expenses. Use form 3903.

Thanks for your prompt reply.
I came and left US on a business visa for 90 days in 2008. So, according to the sustantial presence test, I can apply resident married filing join in March 27th?

1/6 of days in 2008 plus 1/3 of days in 2009 plus days in 2010 must be 183 or more.