The money you hear about people getting for just filing a tax return claiming kids requires you to have some earned income (wages or self employment). Without earned income, you are not eligible for the "refundable" Earned Income Credit or Additional Child Tax Credit.
The Earned Income Credit, on a sliding scale, is available for any amount of earned income. The Additional Child Tax Credit. doesn't start until your have a minimum of $3000 of earned income.
If you are married, you file a joint return with your spouse, and claim the credits based on his income. You cannot get anything filing a separate return from him.