It was introduced in the last budget. Here is an excerpt from the government website:
Eligibility criteria for the Child amount - If a child born in 1990 or later resides with both parents throughout the year, either parent (but not both) may claim $2,000 per child. Any unused portion can be transferred to that parent's spouse or common-law partner. If the child does not reside with both parents throughout the year, the parent who is entitled to claim the amount for an eligible dependant can claim the child amount.
Send this information in writing, or electronically using this notice, to your employer or payers payroll professional. It will be filed with your TD1 Personal Tax Credits Return, and the amount of tax deducted from each pay will be reduced. This change will remain in effect until you advise us that you are no longer eligible to claim the child amount.
If you do not give this information to your employer, your tax deducted at source will not be reduced. However, you will still be able to claim the child amount when you file your T1 Income Tax and Benefit Return for 2007.
Payroll professional: Please file this notice in the employees personnel/pay file as a record of the request for the child amount deduction at source.
If you are eligible to claim other tax credits that will reduce the amount of tax deducted at source, complete and submit a revised TD1 return. To get form TD1 2007 Personal Tax Credits Return visit
http://www.cra-arc.gc.ca/E/pbg/tf/td1/README.html or call 1-800-959-2221.
There is no income requirement. I got a letter from my employer last month asking if I wanted to change my TD1 to reflect this deduction - $2,000 per child, which works out to about a $440 tax decrease per child for the year.
Here is the CRA link:
http://www.cra-arc.gc.ca/agency/budget/2007/taxcredit-e.html