Hi, Is it illegal to do this? I heard this was "cheating the system"
My wife and I have 3 kids together and I always filled my taxes with an ITIN number, due to my immigration status I could not claim the children, however this year my immigration status is now fixed and Now I have a social security number.

Can I claim the child taz credit I did not receive from the previous 3 years?

The ITIN does NOT prevent filing for the Child Tax Credit!

I apply for and GET the Child Tax credit for hundreds of clients every year with one or both of the parents having ITINs, as well as children.

The credit you cannot get with an ITIN is the Earned Income Credit, and amending old returns to get the EIC IS cheating.

So if you have been denying yourself the Child Tax Credit since 2008, amend the returns to get it. Do 2008 FIRST, because the ABSOLUTE deadline for that amendment is 15 April 2012.

If you want my professional help, double-click on my title above and scroll down to my profile/signature. You will find my email address and websites there.