Income reported on a form 1099-MISC in box 7 is self-employed income. Self-employed income is subject to income tax and self-employment taxes calculated at 15.3% on 92.65% on the net income. He can deduct expenses such as supplies from this income.
He will have to use TurboTax Deluxe to report this income or TurboTax Self-Employed if he has expenses to deduct.
If he is claimed as your dependent, he has to indicate on his tax return that he can be claimed as a dependent by someone else.
Please read this TurboTax FAQ on how to report this form 1099-MISC:
He has nothing in box 7 and he does this as volunteer work with nominal pay. Is this still taxable?
If he has a 1099-MISC, in which box is the income reported?
If this is just occasional work or a one-time help given by your son, then this can be considered as Other income, and as it was less than $12,000, your son is not required to file a tax return. On the other hand, if this is regular work, this is self-employment income even if it is reported in box 3 and your son must file a tax return and pay self-employment tax.
It was less than 40 hours throughout the year for less than 40 days.
If this was ongoing throughout the year, it is self-employed income and your son has to file a tax return and report it as self-employed income.