If the income is from working and they will receive W-2s, they are not required to file a tax return since a dependents income of up to $6300 will be offset by the standard deduction. If federal income tax was withheld, they should file a return to get a refund. They should indicate on their return that they can be claimed by someone else.
If they will receive a 1099-MISC or no form reporting their income and it is more than $400, they must file a return to pay around 15% self employment taxes. They will not owe any federal income tax.
You would need to check your state tax laws to see if their filing requirement is any different.
Regardless of whether they file or not, you do not enter their income on your tax return.
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