From the
IRS website
Not All Are Eligible
Some taxpayers with children are not eligible for the advance payment, including:
Taxpayers who filed Form 1040EZ, which doesnt provide for claiming dependents or the Child Tax Credit.
Taxpayers who had income that exceeded certain limits.
Taxpayers whose only children were born before 1987.
Taxpayers whose only child was born in 2003.
Taxpayers whose Child Tax Credit and Additional Child Tax Credit for 2002 totaled less than $600 for each qualifying child because of the tax liability and earned income limitations.
The Child Tax Credit begins to phase out for taxpayers with modified adjusted gross income above:
$110,000, if married filing jointly
$55,000, if married filing separately, or
$75,000, for all others.