The choice to file Form 8814 with the parents' return or Form 8615 with the child's return is one to be made by the preparer of the return.

Per IRS Publication 929 Tax Rules for Children and Dependents, page 9: 

The two rules that follow may affect the tax on the unearned income of certain children.

1. If the child’s interest and dividend income (including capital gain distributions) total less than $10,500, the child’s parent may be able to choose to include that income on the parent’s return rather than file a return for the child.
2. If the child’s interest, dividends, and other investment income total more than $2,100, part of that income may be taxed at the parent’s tax rate instead of the child’s tax rate.

For these rules, the term "child" includes a legally adopted child and a stepchild. These rules apply whether or not the child is a dependent.

These rules don't apply if neither of the child’s parents were living at the end of the year.

Below is information to help you determine where to claim your child's investment income and what form to use for that reporting.

Federal Form 8615 Tax for Certain Children Who Have Unearned Income

 To enter the amounts in the TaxAct® program which will transfer to Form 8615:

1. From within your TaxAct return (Online or Desktop), click Federal. On smaller devices, click the menu icon in the upper left-hand corner, then select Federal
2. Click Taxes in the middle of the screen to expand the category, then click Tax on Child's Investment Income
3. The program will proceed with the interview questions for you to enter or review the appropriate information

Per the IRS Instructions for Form 8615 Tax for Certain Children Who Have Unearned Income, page 1:

Purpose of Form
For children under age 18 and certain older children described below in Who Must File, unearned income over $2,100 is taxed at the parent's rate if the parent's rate is higher than the child's. If the child's unearned income is more than $2,100, use Federal Form 8615 to figure the child's tax.

Unearned Income
For Form 8615, "unearned income" includes all taxable income other than earned income as defined later. Unearned income includes taxable interest, ordinary dividends, capital gains (including capital gain distributions), rents, royalties, etc. It also includes taxable social security benefits, pension and annuity income, taxable scholarship and fellowship grants not reported on Form W-2, unemployment compensation, alimony, and income (other than earned income) received as the beneficiary of a trust.

Who Must File

Form 8615 must be filed for any child who meets all of the following conditions.

1. The child had more than $2,100 of unearned income.
2. The child is required to file a tax return.
3. The child either:
   1. Was under age 18 at the end of 2018,
   2. Was age 18 at the end of 2018 and didn't have earned income that was more than half of the child’s support, or
   3. Was a full-time student at least age 19 and under age 24 at the end of 2018 and did not have earned income that was more than half of the child’s support.
4. At least one of the child’s parents was alive at the end of 2018.
5. The child doesn't file a joint return for 2018.

For these rules, the term "child" includes a legally adopted child and a stepchild. These rules apply whether or not the child is a dependent. These rules don't apply if neither of the child’s parents were living at the end of the year.

Support. Your child’s support includes all amounts spent to provide the child with food, lodging, clothing, education, medical and dental care, recreation, transportation, and similar necessities. To figure your child’s support, count support provided by you, your child, and others. However, a scholarship received by your child isn't considered support if your child is a full-time student. For details, see Pub. 501 Dependents, Standard Deduction, and Filing Information.

TIP: The parent may be able to elect to report the child’s interest, ordinary dividends, and capital gain distributions on the parent’s return. If the parent makes this election, the child won't have to file a return or Form 8615. However, the federal income tax on the child’s income, including qualified dividends and capital gain distributions, may be higher if this election is made. For more details, see Form 8814 Parents’ Election To Report Child’s Interest and Dividends.
 

Federal Form 8814 Parents' Election to Report Child's Interest and Dividends

To enter the amounts in the TaxAct Program which will transfer to Form 8814:

1. From within your TaxAct return (Online or Desktop), click Federal. On smaller devices, click the menu icon in the upper left-hand corner, then select Federal
2. Click Taxes in the middle of the screen to expand the category, then click Child's Interest and Dividend Income on Your Return
3. The program will proceed with the interview questions for you to enter or review the appropriate information

If your child is required to file a return, you may elect to include your child's interest and dividend income on your return if ALL of the following conditions are met, per IRS Publication 929 Tax Rules for Children and Dependents, page 9: 

Parent’s Election To Report Child’s Interest and Dividends. You may be able to elect to include your child’s interest and dividend income (including capital gain distributions) on your tax return. If you do, your child won't have to file return.

• Your child was under age 19 (or under age 24 if a full-time student) at the end of the year.
• Your child had income only from interest and dividends (including capital gain distributions and Alaska Permanent Fund dividends).
• The child’s gross income was less than $10,500.
• The child is required to file a return unless you make this election.
• The child doesn't file a joint return for the year.
• No estimated tax payment was made for the year, and no overpayment from the previous year (or from any amended return) was applied to this year under your child’s name and social security number.
• No federal income tax was taken out of your child’s income under the backup withholding rules.
• You are the parent whose return must be used when applying the special tax rules for children.

You, the parent must also qualify. Per IRS Instructions for Form 8814, page 3: 

Parents who qualify to make the election. You qualify to make this election if you file Form 1040 or Form 1040NR and any of the following apply.

• You are filing a joint return for 2018 with the child’s other parent.
• You and the child’s other parent were married to each other but file separate returns for 2018 and you had the higher taxable income.
• You were unmarried, treated as unmarried for federal income tax purposes, or separated from the child’s other parent by a divorce or separate maintenance decree. The child must have lived with you for most of the year (you were the custodial parent). If you were the custodial parent and you remarried, you can make the election on a joint return with your new spouse. But if you and your new spouse do not file a joint return, you qualify to make the election only if you had higher taxable income than your new spouse.

Note. If you and the child’s other parent were not married but lived together during the year with the child, you qualify to make the election only if you are the parent with the higher taxable income.