Can I claim a child tax credit of previous year 2011 now in 2014, which I did not claim on 2011 as my son does not have ITIN and applied first time in 2011.

I came here in US in Feb11th, 2011 and my wife and son joined me later on July 4th, 2011. My wife and I filed taxes, Married jointly as a resident aliens for 2011. My son is living with us here in USA from 2011.

His total days of presence in US for 2011 was 181 days.

When I filed a federal tax at 2011. I did not get child tax credit of my son as he does not have a ITIN at that time. Can I claim his child tax credit now?

Also If I amend my Federal Tax return do I need to amend my state tax too?