The grandchild's, assuming the account is under his Social security number.

You do not report his/her income on your return or the parent's return**. If it has to be reported at all, it goes on his own return. He or she must file a tax return for 2016 if he had any of the following:

1.         Total income (wages, salaries, taxable scholarship etc.) of more than $6,300 (2016).

2.         Unearned income (interest, dividends, capital gains) of more than $1050 (2016).

3.         Unearned income over $350 and gross income of more than $1050

4.         Household employee income (e.g. baby sitting, lawn mowing) over $2000 ($6300 if under age 18)

5.         Other self employment income over $400, including box 7 of a 1099-MISC

 Even if he had less, he is allowed to file if he needs to get back income tax withholding. He cannot get back social security or Medicare tax withholding.

 He doesn’t get his own $4050 exemption (deduction), when he files. In TurboTax, he indicates that somebody else can claim him as a dependent, at the personal information section.

**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 the parent's (or whomever claims him as a dependent) return, using form 8814. If he has capital gains on a 1099-B, you cannot use this method.

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.