There's no free money and you likely owe tax, 10-30% of your income. And, depending on how much you made, your SSDI may be partly taxable as well.
If you work in someone's home according to their instructions, you are their household employee. You are supposed to receive a W-2 for your wages, and your employer is supposed to pay and withhold household employee tax (this is social security and medicare tax like a normal employee). If they paid you cash under the table, you are still required to report the income, you will owe tax plus the 7.65% social security they did not withhold. We can tell you the procedure for this.
Or, if you worked in your home and took day care clients according to your own interests, then you are self-employed. You file a schedule C as a small business. You report all your gross income (including cash and checks), you can deduct legitimate expenses (including part of your mortgage or rent, food, utilities and so on, since you are using your home for business) and you pay income tax and self-employment tax on the net profit. We can also provide more details about how to do this.
If SSDI is your only income it is not taxable, but if you have other income (from investments, a pension, or a side job) then your SSDI might also be partly taxable. That will be calculated on your tax return.
If you owe and pay tax, you might be eligible for some credits or deductions that would reduce your tax, depending on all your tax information. We can't tell you about a renters credit, since that is only for state income tax and we don't know what state you are in so we can't comment on the rules or amount of any renters credit.
The income tax system is mostly an honors system. If you work under the table and don't report the income, you probably won't get caught, only about 1% of taxpayers are audited. But if you are audited, they can go back through all the years you never filed a tax return, and assess back taxes, interest, and penalties.
