Earned Income Credit

[BallsDeep81]

Im 72 and receive Social Security, I have legal guardianship of of two minors ages 15 and 16 whom receive Survivor Benefits. The minor children have never been claimed for earned income credit nor have I had to file taxes because of my social security awards. My question is this.... Am I losing out on the opportunity to get back a refund based on claiming earned income credit and how far back can I legally file for this refund? 

[VolvoGirl]

Do you any other income?  You need earned income from W2 wages or a Net Profit on Schedule C for self employment income.