You NEVER report a child's income earned from working on your tax return. Income earned from working is only ever reported on a tax return in that person's own name. (Sometimes, if a child's ONLY income is from investments, it can be included on a parent's return, but not if the income is from working.)
The child will file their own return. In this case, since it is less than $12,400, they are not required to file unless they had withholding and want it refunded. The child must answer "yes, I can be claimed as a dependent by someone else" on their tax return.
A child's income does not, by itself, change their dependent status, as long as they meet the normal qualifying rules.
