Form 8615 will be attached to each child's return to correctly calculate the taxes due on their capital gains. Nothing will change with your return.
The first $1,100 for each child is tax-free. The next $1,100 for each child is taxed at their income rate, which would be 10% for short-term capital gains and 0% for long-term capital gains. The remainder of each child's income would be taxed at your tax rate. For TurboTax to calculate this, you will have to complete your tax return first because you will need your taxable income and filing status, so it is probably easier to complete your tax return first.
Form 8814 is used if you include all the income on your own return. However, this can only be used if your children's income is solely from interest and dividends. Dividends include capital gains distributions, but that is separate from capital gains realized from the sale of stock. For more information on reporting your children's income, see this IRS tax topic.
