This is not intended to be tax advice, and you *must* consult with a professional who can look at your exact situation. But in general:
Be aware that the $600-per-year threshold is simply the cutoff where WE (FC) have to report YOUR income to the IRS.
ANY income you make (whether $20 at a garage sale, selling something on craigslist, or earning $25 from FC) is usually considered taxable income by the IRS. And they usually expect it to be reported (it's self-employment income). Again, I am neither an accountant nor lawyer and this is not tax advice, please seek a professional.