You should not claim your child's W-2 or self-employment income on your return even if you claim him as a dependent.

If your dependent earned more than $6,350 in W-2 wages or more than $400 in self-employment/1099/MISC income, he/she is required to file a rerun. For less W-2 income earned, the dependent may elect to file a return to obtain a refund of his/her withholding(s)

If the dependent files his own return with TurboTax, he should check the box Someone else can claim me on their tax return in the personal information section.

See How Do I Add a Dependent's W-2 On My Return?