How can I file a separate tax return for my daughter who is 3 years old with a 1099B from her brokerage custodial account with $3,500 in capital gains from stock sales?

[Bsch4477]

You must file a return for her. You will have to pay Kiddie tax on some of that gain. 

[rjs]

A TurboTax Online account can only be used for one tax return. To file a tax return for your daughter you will have to create a new separate TurboTax Online account for her. You can use your email address for her account.

It would probably be less expensive to use the TurboTax Desktop software instead of TurboTax Online. You could file both your own tax return and your daughter's tax return with one copy of the desktop software.

By the way, as Bsch4477 pointed out, your daughter will have to pay "kiddie tax." When preparing her tax return you must go through the "Child's Income (Under Age 24)" section of the TurboTax interview.

[Mike9241]

Since you are using online, you'll have to create an account for her. You can not use your account because it can have only one party's return. Doing a second return in the same account overwrites the first.  You will need to complete Form 8615 because the kiddie tax applies. The parents' return should be done first because certain information from it must be entered on the 8615