What is minimum income if any to file for credits?

You won't qualify for most credits without any income, but you can file with $1 of income.   You have to have at least $2500 in earned income to be eligible for the Additional Child Tax Credit.  You can qualify for Earned Income Credit with any earned income.  

 

What is Earned Income? 

 

See the chart here in this link to determine whether or not you are required to file.   

 

Tax Credits