what website can tell me how much child tax credit i will earn for my children?

Answer 1

Are you asking about the Child Tax Credit or the Earned Income Credit
There is no online calculator for the Child Tax Credit, but there is for the Earned Income Credit

http://www.irs.gov/individuals/article/0,,id=96406,00.html

1-800-829-1040

Answer 2

Assuming the child is eligible for the credit, it's $1000 per child if you owe than much tax.

It can only reduce your tax to zero, you don't get the amount left over refunded to you.

An eligible child must be under age 17 at the end of the tax year.