You don't add your childs income to your return. If they need to file a return you would create an account for them. If you use your account, your childs information would overwrite yours. If your childs files his own return, he would check that someone else can claim him/her on their return.
Do I need to file my own taxes if I'm a dependent?
https://ttlc.intuit.com/replies/3302185
