You do not USUALLY** report his/her income on your return. If it has to be reported, at all, it goes on his own return. If your dependent child is under age 19 (or under 24 if a full time student), he or she must file a tax return for 2018 if he had any of the following:
1. Total income (wages, salaries, taxable scholarship etc.) of more than $12,000 ($6350 in 2017).
2. Unearned income (interest, dividends, capital gains) of more than $1050.
3. Unearned income over $350 and gross income of more than $1050
4. Household employee income (e.g. baby sitting, lawn mowing) over $2100 ($12.000 if under age 18)
5. Other self employment income over $400, including box 7 of a 1099-MISC**If his only income is from interest and dividends, Alaska PFD or capital gains distributions shown on a 1099-DIV, there is a provision for entering it on your return, using form 8814. Enter at Less common income / Child's income.
But, it is usually best for him to file a separate return, as qualified dividends and capital gain distributions could be taxed at a higher rate on the parent's return.
However, using Form 8814 may benefit a few parents who are not getting the full Child Tax Credit, as the credit will offset the total tax amount, including the child’s portion of the tax.