Form 8615 is for "kiddie tax" on the child's tax return. The "Child's Income" section in TurboTax will determine whether Form 8615 is required, and will fill it out if it's needed.
Form 8814 is for reporting the child's interest and dividends on the parents' tax return. The question is about capital gains. You cannot use Form 8814 for capital gains. Capital gains have to be reported on the child's tax return.
