You don't include their income on your return. It would only go on their return if they are required to file one. They don't have to file if they only have W2 income under 12,400 but can file to get back any withholding taken out in boxes 2 or 17. But you don't get boxes 4 or 6 back.
To file a separate return for a dependent in the Online version you need to set up a new account separate from the parents. Online is only good for one return per account. You can use the same email address for 5 accounts. You can probably use the Free Edition or the Free File website
Https://ttlc.intuit.com/questions/1894512-how-do-i-start-another-return-in-turbotax-online
Be sure on the dependent return you check the box that says you can be claimed on someone else’s return. If your only income is W2 and under 12,400 you do not have to file a return except to get back any withholding taken out.
Filing requirements for a dependent
https://ttlc.intuit.com/community/children-dependents/help/do-i-need-to-file-my-own-taxes-if-i-m-a-d...
