Someone commented on a tax blog that the minimum amount of tax for which IRS will issue a CP-2000 is $500 -- which would mean about $3,300 of 1099-NEC income.  I think I've seen cases where it was $400, but those might be where it starts out above $500 and by the time IRS puts some work into it, they decide not to drop it.  

At least $1,700 is enough for the kid to earn a quarter of Social Security coverage if he pays the SE tax.  If it were under $1,410 you would have to explain that it might be a contribution to herd immunity to senior poverty, but there is no personal benefit.