You don't include their income on your return. It would only go on their return if they are required to file one. To file a separate return for your dependent you need to set up a new account. Online is only good for one return per account. You can use the same email address for 5 accounts. They can probably use the Free Edition. Start another Online return here. Sign up and start a new account.
https://turbotax.intuit.com/personal-taxes/online
You can still claim them on your return. Be sure on their return they check the box that says they can be claimed on someone else’s return. If their only income is W2 and under 13,850 they 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-dependent/00/26111