What forms do I fill out of the only income I receive is Social security supplemental income I have 3 kids 11 10 and 3

If you only get Social Security or SS Disability or ssi or a SSA-1099 it is not taxable and you don't need to file a return.  If you get a 1095-A for Marketplace health insurance you do need to file.  If you don't have any earned income from working or self employment you can't get any credits like the Child Tax Credit or EIC.  

There has only been one tax year for which you could receive the child tax credit even if you did not work --- that was several years ago.   Under the current tax laws, if your only income is SSI, you are not eligible for child-related credits like earned income credit or child tax credit.   In order to receive those credits you must have income from working.