Yes a 1099NEC is for contractor self employment income. They are not an employee. They will file it on Schedule C in their personal tax return. They will pay self employment tax on it in addition to any regular income tax on it. The SE tax is 15.3% on 92.35% of the net profit on Schedule C. So $6203 x .9235 = 5,728.47. Then 5,728.47 x .153 = 876.46.
Don't know about the second minor trying to file. Would need more info like what the error message is. Being a minor doesn't matter to file taxes.
