You do not enter your children's income on your tax return. They have to file their own tax returns to report their income. When they do that, make sure they check the box that says someone can claim them as a dependent.
A TurboTax Online account can be used for only one person (or one married couple filing jointly). If your adult children want to use TurboTax Online to file their tax returns, they cannot use your account. They have to each create an account of their own. If you are going to use TurboTax Online to prepare your children's tax returns for them, you cannot use the same account that you used for your own tax return. You have to create a separate account for each child.
You mentioned that they are "adults"----do they still meet the criteria to be claimed as your dependents? If so, you can claim them on your own tax return, and if they have income to enter, they prepare and file their own returns and must say in MY INFO that they can be claimed as someone else's dependent. You do not enter their income on your own return.
IRS interview to help determine who can be claimed:
https://www.irs.gov/help/ita/who-can-i-claim-as-a-dependent
When you use Online TurboTax, you get one return per fee. Each return needs its own account and user ID. If you use the same account and user ID for a second return, you overwrite the first one and lose it forever.
https://turbotax.intuit.com/personal-taxes/online/
When you use Desktop TurboTax, which you install from a CD or download to your own hard drive, you can prepare and e-file multiple returns for the cost of the software. You can e-file up to 5 Federal returns—more if you mail the additional ones. If you have multiple returns to prepare for family members, Desktop is more cost effective.
Desktop --unless you specifically buy federal Deluxe only from a retailer-- will include the software for one specific state. You can prepare as many returns for that state as the number of federal returns you prepare. E-filing state returns is an extra fee which can be avoided by printing and mailing the states. Additional--other--state software is an additional fee for the software.