The income earned by an UTMA account belongs to your child, so you have a choice.  If your child is younger than age 19 or a full-time student age 19-23, he or she must file a tax return for 2016 if he or she had any of the following:

 - Unearned income (interest, dividends, capital gains, taxable scholarships, unemployment compensation) of more than $1,050.

 - Earned income (wages, salaries, tips, and fees) of more than $6,300.

 - Gross income (earned and unearned income) was more than the larger of:

  $1,050 or earned income (up to $6,300) plus $350

If your child is younger than 19 or a full-time student age 19-23 and is required to file a return, you may be able to report the child's unearned income on your return using Form 8814, Parent's Election to Report Child's Interest and Dividends. If you do, the child is not required to file a return.  However, in most cases it's better to report the income on the child's return to avoid taxes on the gain.

If you decide not to report your child's income on your return, or you don't qualify to use Form 8814, the child must file a return, and may have to file Form 8615, Tax for Certain Children who have Unearned Income of More Than $2,100.