It is correct, your son is not paying any federal income taxes if his income is under $12,000 but he is subject to self-employment taxes (social security and medicare taxes) on the 1099 income. Self employment taxes are 15.3% of the net profit of his business.
<a rel="nofollow" target="_blank" href="
https://turbotax.intuit.com/tax-tips/self-employment-taxes/the-self-employment-tax/L8xXjolB4">https:...>
